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Metadata in HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals">HTML text fundamentals</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks">Creating hyperlinks</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Advanced_text_formatting">Advanced text formatting</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure">Document and website structure</a></li><li><em><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML" aria-current="page">Debugging HTML</a></em></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter">Marking up a letter</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Structuring_a_page_of_content">Structuring a page of content</a></li></ol></details></li><li><details><summary>Multimedia and embedding</summary><ol><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding">Multimedia and embedding</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Images_in_HTML">Images in HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Video_and_audio_content">Video and audio content</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Other_embedding_technologies">From object to iframe — other embedding technologies</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Adding_vector_graphics_to_the_Web">Adding vector graphics to the web</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images">Responsive images</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Mozilla_splash_page">Mozilla splash page</a></li></ol></details></li><li><details><summary>HTML tables</summary><ol><li><a href="/en-US/docs/Learn/HTML/Tables">HTML tables</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Basics">HTML table basics</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Advanced">HTML table advanced features and accessibility</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Structuring_planet_data">Structuring planet data</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/CSS">CSS — Styling the web</a></li><li><details><summary>CSS first steps</summary><ol><li><a href="/en-US/docs/Learn/CSS/First_steps">CSS first steps</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/What_is_CSS">What is CSS?</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/Getting_started">Getting started with CSS</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/How_CSS_is_structured">How CSS is structured</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/How_CSS_works">How CSS works</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/Styling_a_biography_page">Styling a biography page</a></li></ol></details></li><li><details><summary>CSS building blocks</summary><ol><li><a href="/en-US/docs/Learn/CSS/Building_blocks">CSS building blocks</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors">CSS selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Type_Class_and_ID_Selectors">Type, class, and ID selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Attribute_selectors">Attribute selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements">Pseudo-classes and pseudo-elements</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators">Combinators</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance">Cascade, specificity, and inheritance</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Cascade_layers">Cascade layers</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/The_box_model">The box model</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Backgrounds_and_borders">Backgrounds and borders</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Handling_different_text_directions">Handling different text directions</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Overflowing_content">Overflowing content</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Values_and_units">CSS values and units</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Sizing_items_in_CSS">Sizing items in CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Images_media_form_elements">Images, media, and form elements</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Styling_tables">Styling tables</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Advanced_styling_effects">Advanced styling effects</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Debugging_CSS">Debugging CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Organizing">Organizing your CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Fundamental_CSS_comprehension">Fundamental CSS comprehension</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Creating_fancy_letterheaded_paper">Creating fancy letterheaded paper</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/A_cool_looking_box">A cool-looking box</a></li></ol></details></li><li><details><summary>Styling text</summary><ol><li><a href="/en-US/docs/Learn/CSS/Styling_text">CSS styling text</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Fundamentals">Fundamental text and font styling</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Styling_lists">Styling lists</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Styling_links">Styling links</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Web_fonts">Web fonts</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Typesetting_a_homepage">Typesetting a community school homepage</a></li></ol></details></li><li><details><summary>CSS layout</summary><ol><li><a href="/en-US/docs/Learn/CSS/CSS_layout">CSS layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Introduction">Introduction to CSS layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Normal_Flow">Normal Flow</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Flexbox">Flexbox</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Grids">Grids</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Floats">Floats</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Positioning">Positioning</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Multiple-column_Layout">Multiple-column layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design">Responsive design</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Media_queries">Beginner's guide to media queries</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Legacy_Layout_Methods">Legacy layout methods</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Supporting_Older_Browsers">Supporting older browsers</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Fundamental_Layout_Comprehension">Fundamental layout comprehension</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/JavaScript">JavaScript — Dynamic client-side scripting</a></li><li><details><summary>JavaScript first steps</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/First_steps">JavaScript first steps</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/What_is_JavaScript">What is JavaScript?</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/A_first_splash">A first splash into JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/What_went_wrong">What went wrong? Troubleshooting JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Variables">Storing the information you need — Variables</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Math">Basic math in JavaScript — numbers and operators</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Strings">Handling text — strings in JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods">Useful string methods</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Arrays">Arrays</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator">Silly story generator</a></li></ol></details></li><li><details><summary>JavaScript building blocks</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks">JavaScript building blocks</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/conditionals">Making decisions in your code — conditionals</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Looping_code">Looping code</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Functions">Functions — reusable blocks of code</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Build_your_own_function">Build your own function</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Return_values">Function return values</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Events">Introduction to events</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Event_bubbling">Event bubbling</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Image_gallery">Image gallery</a></li></ol></details></li><li><details><summary>Introducing JavaScript objects</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Objects">Introducing JavaScript objects</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Basics">JavaScript object basics</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object_prototypes">Object prototypes</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object-oriented_programming">Object-oriented programming</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Classes_in_JavaScript">Classes in JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/JSON">Working with JSON</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object_building_practice">Object building practice</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features">Adding features to our bouncing balls demo</a></li></ol></details></li><li><details><summary>Asynchronous JavaScript</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous">Asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Introducing">Introducing asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Promises">How to use promises</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Implementing_a_promise-based_API">How to implement a promise-based API</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Introducing_workers">Introducing workers</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Sequencing_animations">Sequencing animations</a></li></ol></details></li><li><details><summary>Client-side web APIs</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs">Client-side web APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introduction">Introduction to web APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents">Manipulating documents</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Fetching_data">Fetching data from the server</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Third_party_APIs">Third-party APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Drawing_graphics">Drawing graphics</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs">Video and Audio APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Client-side_storage">Client-side storage</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Forms">Web forms — Working with user data</a></li><li><details><summary>Web form building blocks</summary><ol><li><a href="/en-US/docs/Learn/Forms">Web form building blocks</a></li><li><a href="/en-US/docs/Learn/Forms/Your_first_form">Your first form</a></li><li><a href="/en-US/docs/Learn/Forms/How_to_structure_a_web_form">How to structure a web form</a></li><li><a href="/en-US/docs/Learn/Forms/Basic_native_form_controls">Basic native form controls</a></li><li><a href="/en-US/docs/Learn/Forms/HTML5_input_types">The HTML5 input types</a></li><li><a href="/en-US/docs/Learn/Forms/Other_form_controls">Other form controls</a></li><li><a href="/en-US/docs/Learn/Forms/Styling_web_forms">Styling web forms</a></li><li><a href="/en-US/docs/Learn/Forms/Advanced_form_styling">Advanced form styling</a></li><li><a href="/en-US/docs/Learn/Forms/UI_pseudo-classes">UI pseudo-classes</a></li><li><a href="/en-US/docs/Learn/Forms/Form_validation">Client-side form validation</a></li><li><a href="/en-US/docs/Learn/Forms/Sending_and_retrieving_form_data">Sending form data</a></li></ol></details></li><li><details><summary>Advanced web form techniques</summary><ol><li><a href="/en-US/docs/Learn/Forms/How_to_build_custom_form_controls">How to build custom form controls</a></li><li><a href="/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript">Sending forms through JavaScript</a></li><li><a href="/en-US/docs/Learn/Forms/Property_compatibility_table_for_form_controls">CSS property compatibility table for form controls</a></li><li><a href="/en-US/docs/Learn/Forms/HTML_forms_in_legacy_browsers">HTML forms in legacy browsers</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Accessibility">Accessibility — Make the web usable by everyone</a></li><li><details><summary>Accessibility guides</summary><ol><li><a href="/en-US/docs/Learn/Accessibility">Accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/What_is_accessibility">What is accessibility?</a></li><li><a href="/en-US/docs/Learn/Accessibility/HTML">HTML: A good basis for accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/CSS_and_JavaScript">CSS and JavaScript accessibility best practices</a></li><li><a href="/en-US/docs/Learn/Accessibility/WAI-ARIA_basics">WAI-ARIA basics</a></li><li><a href="/en-US/docs/Learn/Accessibility/Multimedia">Accessible multimedia</a></li><li><a href="/en-US/docs/Learn/Accessibility/Mobile">Mobile accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/Accessibility_troubleshooting">Assessment: Accessibility troubleshooting</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Performance">Performance — Making websites fast and responsive</a></li><li><details><summary>Performance guides</summary><ol><li><a href="/en-US/docs/Learn/Performance">Web performance</a></li><li><a href="/en-US/docs/Learn/Performance/why_web_performance">The "why" of web performance</a></li><li><a href="/en-US/docs/Learn/Performance/What_is_web_performance">What is web performance?</a></li><li><a href="/en-US/docs/Learn/Performance/Perceived_performance">Perceived performance</a></li><li><a href="/en-US/docs/Learn/Performance/Measuring_performance">Measuring performance</a></li><li><a href="/en-US/docs/Learn/Performance/Multimedia">Multimedia: Images</a></li><li><a href="/en-US/docs/Learn/Performance/video">Multimedia: video</a></li><li><a href="/en-US/docs/Learn/Performance/JavaScript">JavaScript performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/HTML">HTML performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/CSS">CSS performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/business_case_for_performance">The business case for web performance</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/MathML">MathML — Writing mathematics with MathML</a></li><li><details><summary>MathML first steps</summary><ol><li><a href="/en-US/docs/Learn/MathML/First_steps">MathML first steps</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Getting_started">Getting started with MathML</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Text_containers">MathML Text Containers</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Fractions_and_roots">MathML fractions and roots</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Scripts">MathML scripted elements</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Tables">MathML tables</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Three_famous_mathematical_formulas">Three famous mathematical formulas</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/../Games">Games — Developing games for the web</a></li><li><details><summary>Guides and tutorials</summary><ol><li><a href="/en-US/docs/Games/Introduction">Introduction to game development for the Web</a></li><li><a href="/en-US/docs/Games/Techniques">Techniques for game development</a></li><li><a href="/en-US/docs/Games/Tutorials">Tutorials</a></li><li><a href="/en-US/docs/Games/Publishing_games">Publishing games</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Tools_and_testing">Tools and testing</a></li><li><details><summary>Client-side web development tools</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools">Understanding client-side web development tools</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Overview">Client-side tooling overview</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Command_line">Command line crash course</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Package_management">Package management basics</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Introducing_complete_toolchain">Introducing a complete toolchain</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Deployment">Deploying our app</a></li></ol></details></li><li><details><summary>Introduction to client-side frameworks</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Introduction">Introduction to client-side frameworks</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Main_features">Framework main features</a></li></ol></details></li><li><details><summary>React</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_getting_started">Getting started with React</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_todo_list_beginning">Beginning our React todo list</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_components">Componentizing our React app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_events_state">React interactivity: Events and state</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_filtering_conditional_rendering">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_accessibility">Accessibility in React</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_resources">React resources</a></li></ol></details></li><li><details><summary>Ember</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_getting_started">Getting started with Ember</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_structure_componentization">Ember app structure and componentization</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_interactivity_events_state">Ember interactivity: Events, classes and state</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_conditional_footer">Ember Interactivity: Footer functionality, conditional rendering</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_routing">Routing in Ember</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_resources">Ember resources and troubleshooting</a></li></ol></details></li><li><details><summary>Vue</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_getting_started">Getting started with Vue</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_first_component">Creating our first Vue component</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_rendering_lists">Rendering a list of Vue components</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_methods_events_models">Adding a new todo form: Vue events, methods, and models</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_styling">Styling Vue components with CSS</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_computed_properties">Using Vue computed properties</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_conditional_rendering">Vue conditional rendering: editing existing todos</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_refs_focus_management">Vue refs and lifecycle methods for focus management</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_resources">Vue resources</a></li></ol></details></li><li><details><summary>Svelte</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_getting_started">Getting started with Svelte</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_Todo_list_beginning">Starting our Svelte to-do list app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_variables_props">Dynamic behavior in Svelte: working with variables and props</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_components">Componentizing our Svelte app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_reactivity_lifecycle_accessibility">Advanced Svelte: Reactivity, lifecycle, accessibility</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_stores">Working with Svelte stores</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_TypeScript">TypeScript support in Svelte</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_deployment_next">Deployment and next steps</a></li></ol></details></li><li><details><summary>Angular</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_getting_started">Getting started with Angular</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_todo_list_beginning">Beginning our Angular todo list app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_styling">Styling our Angular app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_item_component">Creating an item component</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_filtering">Filtering our to-do items</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_building">Building Angular applications and further resources</a></li></ol></details></li><li><details><summary>Git and GitHub</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/GitHub">Git and GitHub</a></li></ol></details></li><li><details><summary>Cross browser testing</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing">Cross browser testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Introduction">Introduction to cross-browser testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Testing_strategies">Strategies for carrying out testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/HTML_and_CSS">Handling common HTML and CSS problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/JavaScript">Handling common JavaScript problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility">Handling common accessibility problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Feature_detection">Implementing feature detection</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Automated_testing">Introduction to automated testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Your_own_automation_environment">Setting up your own test automation environment</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Server-side">Server-side website programming</a></li><li><details><summary>First steps</summary><ol><li><a href="/en-US/docs/Learn/Server-side/First_steps">Server-side website programming first steps</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Introduction">Introduction to the server side</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Client-Server_overview">Client-Server Overview</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Web_frameworks">Server-side web frameworks</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Website_security">Website security</a></li></ol></details></li><li><details><summary>Django web framework (Python)</summary><ol><li><a href="/en-US/docs/Learn/Server-side/Django">Django Web Framework (Python)</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Introduction">Django introduction</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/development_environment">Setting up a Django development environment</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Tutorial_local_library_website">Django Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/skeleton_website">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Models">Django Tutorial Part 3: Using models</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Admin_site">Django Tutorial Part 4: Django admin site</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Home_page">Django Tutorial Part 5: Creating our home page</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Generic_views">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Sessions">Django Tutorial Part 7: Sessions framework</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Authentication">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Forms">Django Tutorial Part 9: Working with forms</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Testing">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Deployment">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/web_application_security">Django web application security</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/django_assessment_blog">Assessment: DIY Django mini blog</a></li></ol></details></li><li><details><summary>Express Web Framework (Node.js/JavaScript)</summary><ol><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs">Express web framework (Node.js/JavaScript)</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Introduction">Express/Node introduction</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/development_environment">Setting up a Node development environment</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Tutorial_local_library_website">Express Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/skeleton_website">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/mongoose">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/routes">Express Tutorial Part 4: Routes and controllers</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Displaying_data">Express Tutorial Part 5: Displaying library data</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/forms">Express Tutorial Part 6: Working with forms</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/deployment">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Common_questions">Further resources</a></li><li><details><summary>Common questions</summary><ol><li><a href="/en-US/docs/Learn/Common_questions">Common questions</a></li><li><a href="/en-US/docs/Learn/HTML/Howto">Use HTML to solve common problems</a></li><li><a href="/en-US/docs/Learn/CSS/Howto">Use CSS to solve common problems</a></li><li><a href="/en-US/docs/Learn/JavaScript/Howto">Solve common problems in your JavaScript code</a></li><li><a href="/en-US/docs/Learn/Common_questions/Web_mechanics">Web mechanics</a></li><li><a href="/en-US/docs/Learn/Common_questions/Tools_and_setup">Tools and setup</a></li><li><a href="/en-US/docs/Learn/Common_questions/Design_and_accessibility">Design and accessibility</a></li></ol></details></li></ol></div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#debugging_isnt_scary">Debugging isn't scary</a></li><li class="document-toc-item "><a class="document-toc-link" href="#html_and_debugging">HTML and debugging</a></li><li class="document-toc-item "><a class="document-toc-link" href="#summary">Summary</a></li></ul></section></div></nav></aside><section class="place side"></section></div></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>Debugging HTML</h1></header><div class="section-content"><ul class="prev-next"> <li><a class="button secondary" href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure"><span class="button-wrap"> Previous </span></a></li> <li><a class="button secondary" href="/en-US/docs/Learn/HTML/Introduction_to_HTML"><span class="button-wrap"> Overview: Introduction to HTML</span></a></li> <li><a class="button secondary" href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter"><span class="button-wrap"> Next </span></a></li> </ul> <p>Writing HTML is fine, but what if something goes wrong, and you can't work out where the error in the code is? This article will introduce you to some tools that can help you find and fix errors in HTML.</p> <figure class="table-container"><table> <tbody> <tr> <th scope="row">Prerequisites:</th> <td> HTML familiarity, as covered in, for example, <a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started">Getting started with HTML</a>, <a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals">HTML text fundamentals</a>, and <a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks">Creating hyperlinks</a>. </td> </tr> <tr> <th scope="row">Objective:</th> <td>Learn the basics of using debugging tools to find problems in HTML.</td> </tr> </tbody> </table></figure></div><section aria-labelledby="debugging_isnt_scary"><h2 id="debugging_isnt_scary"><a href="#debugging_isnt_scary">Debugging isn't scary</a></h2><div class="section-content"><p>When writing code of some kind, everything is usually fine, until that dreaded moment when an error occurs — you've done something wrong, so your code doesn't work — either not at all, or not quite how you wanted it to. For example, the following shows an error reported when trying to <a href="/en-US/docs/Glossary/Compile">compile</a> a simple program written in the <a href="https://www.rust-lang.org/" class="external" target="_blank">Rust</a> language.</p> <p> <img src="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/error-message.png" alt="A console window showing the result of trying to compile a rust program with a missing quote around a string in a print statement. The error message reported is error: unterminated double quote string." width="711" height="520" loading="lazy"> </p> <p>Here, the error message is relatively easy to understand — "unterminated double quote string". If you look at the listing, you can probably see how <code>println!(Hello, world!");</code> might logically be missing a double quote. However, error messages can quickly get more complicated and less easy to interpret as programs get bigger, and even simple cases can look a little intimidating to someone who doesn't know anything about Rust.</p> <p>Debugging doesn't have to be scary though — the key to being comfortable with writing and debugging any programming language or code is familiarity with both the language and the tools.</p></div></section><section aria-labelledby="html_and_debugging"><h2 id="html_and_debugging"><a href="#html_and_debugging">HTML and debugging</a></h2><div class="section-content"><p>HTML is not as complicated to understand as Rust. HTML is not compiled into a different form before the browser parses it and shows the result (it is <em>interpreted</em>, not <em>compiled</em>). And HTML's <a href="/en-US/docs/Glossary/Element">element</a> syntax is arguably a lot easier to understand than a "real programming language" like Rust, <a href="/en-US/docs/Glossary/JavaScript">JavaScript</a>, or <a href="/en-US/docs/Glossary/Python">Python</a>. The way that browsers parse HTML is a lot more <strong>permissive</strong> than how programming languages are run, which is both a good and a bad thing.</p></div></section><section aria-labelledby="permissive_code"><h3 id="permissive_code"><a href="#permissive_code">Permissive code</a></h3><div class="section-content"><p>So what do we mean by permissive? Well, generally when you do something wrong in code, there are two main types of error that you'll come across:</p> <ul> <li><strong>Syntax errors</strong>: These are spelling or punctuation errors in your code that actually cause the program not to run, like the Rust error shown above. These are usually easy to fix as long as you are familiar with the language's syntax and know what the error messages mean.</li> <li><strong>Logic errors</strong>: These are errors where the syntax is actually correct, but the code is not what you intended it to be, meaning that the program runs incorrectly. These are often harder to fix than syntax errors, as there isn't an error message to direct you to the source of the error.</li> </ul> <p>HTML itself doesn't suffer from syntax errors because browsers parse it permissively, meaning that the page still displays even if there are syntax errors. Browsers have built-in rules to state how to interpret incorrectly written markup, so you'll get something running, even if it is not what you expected. This, of course, can still be a problem!</p> <div class="notecard note"> <p><strong>Note:</strong> HTML is parsed permissively because when the web was first created, it was decided that allowing people to get their content published was more important than making sure the syntax was absolutely correct. The web would probably not be as popular as it is today, if it had been more strict from the very beginning.</p> </div></div></section><section aria-labelledby="active_learning_studying_permissive_code"><h3 id="active_learning_studying_permissive_code"><a href="#active_learning_studying_permissive_code">Active learning: Studying permissive code</a></h3><div class="section-content"><p>It's time to study the permissive nature of HTML code.</p> <ol> <li> <p>First, download our <a href="https://github.com/mdn/learning-area/blob/main/html/introduction-to-html/debugging-html/debug-example.html" class="external" target="_blank">debug-example demo</a> and save it locally. This demo is deliberately written with some built-in errors for us to explore (the HTML markup is said to be <strong>badly-formed</strong>, as opposed to <strong>well-formed</strong>).</p> </li> <li> <p>Next, open it in a browser. You will see something like this: <img src="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/badly-formed-html.png" alt="A simple HTML document with a title of HTML debugging examples, and some information about common HTML errors, such as unclosed elements, badly nested elements, and unclosed attributes. " width="626" height="498" loading="lazy"> </p> </li> <li> <p>This immediately doesn't look great; let's look at the source code to see if we can work out why (only the body contents are shown):</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><h1>HTML debugging examples</h1> <p>What causes errors in HTML? <ul> <li>Unclosed elements: If an element is <strong>not closed properly, then its effect can spread to areas you didn't intend <li>Badly nested elements: Nesting elements properly is also very important for code behaving correctly. <strong>strong <em>strong emphasized?</strong> what is this?</em> <li>Unclosed attributes: Another common source of HTML problems. Let's look at an example: <a href="https://www.mozilla.org/>link to Mozilla homepage</a> </ul> </code></pre></div> </li> <li> <p>Let's review the problems:</p> <ul> <li>The <a href="/en-US/docs/Web/HTML/Element/p">paragraph</a> and <a href="/en-US/docs/Web/HTML/Element/li">list item</a> elements have no closing tags. Looking at the image above, this doesn't seem to have affected the markup rendering too badly, as it is easy to infer where one element should end and another should begin.</li> <li>The first <a href="/en-US/docs/Web/HTML/Element/strong"><code><strong></code></a> element has no closing tag. This is a bit more problematic, as it isn't easy to tell where the element is supposed to end. In fact, the whole of the rest of the text has been strongly emphasized.</li> <li>This section is badly nested: <code><strong>strong <em>strong emphasized?</strong> what is this?</em></code>. It is not easy to tell how this has been interpreted because of the previous problem.</li> <li>The <a href="/en-US/docs/Web/HTML/Element/a#href"><code>href</code></a> attribute value is missing a closing double quote. This seems to have caused the biggest problem — the link has not rendered at all.</li> </ul> </li> <li> <p>Now let's look at the markup the browser has rendered, as opposed to the markup in the source code. To do this, we can use the browser developer tools. If you are not familiar with how to use your browser's developer tools, take a few minutes to review <a href="/en-US/docs/Learn/Common_questions/Tools_and_setup/What_are_browser_developer_tools">Discover browser developer tools</a>.</p> </li> <li> <p>In the DOM inspector, you can see what the rendered markup looks like: <img src="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/html-inspector.png" alt="The HTML inspector in Firefox, with our example's paragraph highlighted, showing the text "What causes errors in HTML?" Here you can see that the paragraph element has been closed by the browser." width="851" height="715" loading="lazy"> </p> </li> <li> <p>Using the DOM inspector, let's explore our code in detail to see how the browser has tried to fix our HTML errors (we did the review in Firefox; other modern browsers <em>should</em> give the same result):</p> <ul> <li> <p>The paragraphs and list items have been given closing tags.</p> </li> <li> <p>It isn't clear where the first <code><strong></code> element should be closed, so the browser has wrapped each separate block of text with its own strong tag, right down to the bottom of the document!</p> </li> <li> <p>The incorrect nesting has been fixed by the browser as shown here:</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><strong> strong <em>strong emphasized?</em> </strong> <em> what is this?</em> </code></pre></div> </li> <li> <p>The link with the missing double quote has been deleted altogether. The last list item looks like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><li> <strong> Unclosed attributes: Another common source of HTML problems. Let's look at an example: </strong> </li> </code></pre></div> </li> </ul> </li> </ol></div></section><section aria-labelledby="html_validation"><h3 id="html_validation"><a href="#html_validation">HTML validation</a></h3><div class="section-content"><p>So you can see from the above example that you really want to make sure your HTML is well-formed! But how? In a small example like the one seen above, it is easy to search through the lines and find the errors, but what about a huge, complex HTML document?</p> <p>The best strategy is to start by running your HTML page through the <a href="https://validator.w3.org/" class="external" target="_blank">Markup Validation Service</a> — created and maintained by the W3C, the organization that looks after the specifications that define HTML, CSS, and other web technologies. This webpage takes an HTML document as an input, goes through it, and gives you a report to tell you what is wrong with your HTML.</p> <p> <img src="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/validator.png" alt="The HTML validator homepage" width="1105" height="776" loading="lazy"> </p> <p>To specify the HTML to validate, you can provide a web address, upload an HTML file, or directly input some HTML code.</p></div></section><section aria-labelledby="active_learning_validating_an_html_document"><h3 id="active_learning_validating_an_html_document"><a href="#active_learning_validating_an_html_document">Active learning: Validating an HTML document</a></h3><div class="section-content"><p>Let's try this with our <a href="https://github.com/mdn/learning-area/blob/main/html/introduction-to-html/debugging-html/debug-example.html" class="external" target="_blank">sample document</a>.</p> <ol> <li>First, load the <a href="https://validator.w3.org/" class="external" target="_blank">Markup Validation Service</a> in one browser tab, if it isn't already open.</li> <li>Switch to the <a href="https://validator.w3.org/#validate_by_input" class="external" target="_blank">Validate by Direct Input</a> tab.</li> <li>Copy all of the sample document's code (not just the body) and paste it into the large text area shown in the Markup Validation Service.</li> <li>Press the <em>Check</em> button.</li> </ol> <p>This should give you a list of errors and other information.</p> <p> <img src="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/validation-results.png" alt="A list of HTML validation results from the W3C markup validation service" width="603" height="535" loading="lazy"> </p> <h4 id="interpreting_the_error_messages">Interpreting the error messages</h4> <p>The error messages are usually helpful, but sometimes they are not so helpful; with a bit of practice you can work out how to interpret these to fix your code. Let's go through the error messages and see what they mean. You'll see that each message comes with a line and column number to help you to locate the error easily.</p> <ul> <li> <p>"End tag <code>li</code> implied, but there were open elements" (2 instances): These messages indicate that an element is open that should be closed. The ending tag is implied, but not actually there. The line/column information points to the first line after the line where the closing tag should really be, but this is a good enough clue to see what is wrong.</p> </li> <li> <p>"Unclosed element <code>strong</code>": This is really easy to understand — a <a href="/en-US/docs/Web/HTML/Element/strong"><code><strong></code></a> element is unclosed, and the line/column information points right to where it is.</p> </li> <li> <p>"End tag <code>strong</code> violates nesting rules": This points out the incorrectly nested elements, and the line/column information points out where they are.</p> </li> <li> <p>"End of file reached when inside an attribute value. Ignoring tag": This one is rather cryptic; it refers to the fact that there is an attribute value not properly formed somewhere, possibly near the end of the file because the end of the file appears inside the attribute value. The fact that the browser doesn't render the link should give us a good clue as to what element is at fault.</p> </li> <li> <p>"End of file seen and there were open elements": This is a bit ambiguous, but basically refers to the fact there are open elements that need to be properly closed. The line numbers point to the last few lines of the file, and this error message comes with a line of code that points out an example of an open element:</p> <pre class="brush: plain notranslate">example: <a href="https://www.mozilla.org/>link to Mozilla homepage</a> ↩ </ul>↩ </body>↩</html> </pre> <div class="notecard note"> <p><strong>Note:</strong> An attribute missing a closing quote can result in an open element because the rest of the document is interpreted as the attribute's content.</p> </div> </li> <li> <p>"Unclosed element <code>ul</code>": This is not very helpful, as the <a href="/en-US/docs/Web/HTML/Element/ul"><code><ul></code></a> element <em>is</em> closed correctly. This error comes up because the <a href="/en-US/docs/Web/HTML/Element/a"><code><a></code></a> element is not closed, due to the missing closing quote mark.</p> </li> </ul> <p>If you can't work out what every error message means, don't worry about it — a good idea is to try fixing a few errors at a time. Then try revalidating your HTML to show what errors are left. Sometimes fixing an earlier error will also get rid of other error messages — several errors can often be caused by a single problem, in a domino effect.</p> <p>You will know when all your errors are fixed when you see the following banner in your output:</p> <p> <img src="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/valid-html-banner.png" alt="Banner that reads "The document validates according to the specified schema(s) and to additional constraints checked by the validator."" width="934" height="46" loading="lazy"> </p></div></section><section aria-labelledby="summary"><h2 id="summary"><a href="#summary">Summary</a></h2><div class="section-content"><p>So there we have it, an introduction to debugging HTML, which should give you some useful skills to count on when you start to debug CSS, JavaScript, and other types of code later on in your career. 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Content available under <a href="/en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML","doc":{"isMarkdown":true,"isTranslated":false,"isActive":true,"flaws":{},"title":"Debugging HTML","mdn_url":"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML","locale":"en-US","native":"English (US)","sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Learn/Getting_started_with_the_web\">Complete beginners start here!</a></li><li><details><summary>Getting started with the web</summary><ol><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web\">Getting started with the web</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Installing_basic_software\">Installing basic software</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/What_will_your_website_look_like\">What will your website look like?</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Dealing_with_files\">Dealing with files</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/HTML_basics\">HTML basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/CSS_basics\">CSS basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics\">JavaScript basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Publishing_your_website\">Publishing your website</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/How_the_Web_works\">How the web works</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/HTML\">HTML — Structuring the web</a></li><li><details open=\"\"><summary>Introduction to HTML</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML\">Introduction to HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started\">Getting started with HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/The_head_metadata_in_HTML\">What's in the head? Metadata in HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals\">HTML text fundamentals</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks\">Creating hyperlinks</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Advanced_text_formatting\">Advanced text formatting</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure\">Document and website structure</a></li><li><em><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML\" aria-current=\"page\">Debugging HTML</a></em></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter\">Marking up a letter</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Structuring_a_page_of_content\">Structuring a page of content</a></li></ol></details></li><li><details><summary>Multimedia and embedding</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding\">Multimedia and embedding</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Images_in_HTML\">Images in HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Video_and_audio_content\">Video and audio content</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Other_embedding_technologies\">From object to iframe — other embedding technologies</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Adding_vector_graphics_to_the_Web\">Adding vector graphics to the web</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images\">Responsive images</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Mozilla_splash_page\">Mozilla splash page</a></li></ol></details></li><li><details><summary>HTML tables</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Tables\">HTML tables</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Basics\">HTML table basics</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Advanced\">HTML table advanced features and accessibility</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Structuring_planet_data\">Structuring planet data</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/CSS\">CSS — Styling the web</a></li><li><details><summary>CSS first steps</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/First_steps\">CSS first steps</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/What_is_CSS\">What is CSS?</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/Getting_started\">Getting started with CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/How_CSS_is_structured\">How CSS is structured</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/How_CSS_works\">How CSS works</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/Styling_a_biography_page\">Styling a biography page</a></li></ol></details></li><li><details><summary>CSS building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks\">CSS building blocks</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors\">CSS selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Type_Class_and_ID_Selectors\">Type, class, and ID selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Attribute_selectors\">Attribute selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements\">Pseudo-classes and pseudo-elements</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators\">Combinators</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance\">Cascade, specificity, and inheritance</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Cascade_layers\">Cascade layers</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/The_box_model\">The box model</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Backgrounds_and_borders\">Backgrounds and borders</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Handling_different_text_directions\">Handling different text directions</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Overflowing_content\">Overflowing content</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Values_and_units\">CSS values and units</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Sizing_items_in_CSS\">Sizing items in CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Images_media_form_elements\">Images, media, and form elements</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Styling_tables\">Styling tables</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Advanced_styling_effects\">Advanced styling effects</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Debugging_CSS\">Debugging CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Organizing\">Organizing your CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Fundamental_CSS_comprehension\">Fundamental CSS comprehension</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Creating_fancy_letterheaded_paper\">Creating fancy letterheaded paper</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/A_cool_looking_box\">A cool-looking box</a></li></ol></details></li><li><details><summary>Styling text</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/Styling_text\">CSS styling text</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Fundamentals\">Fundamental text and font styling</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Styling_lists\">Styling lists</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Styling_links\">Styling links</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Web_fonts\">Web fonts</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Typesetting_a_homepage\">Typesetting a community school homepage</a></li></ol></details></li><li><details><summary>CSS layout</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout\">CSS layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Introduction\">Introduction to CSS layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Normal_Flow\">Normal Flow</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Flexbox\">Flexbox</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Grids\">Grids</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Floats\">Floats</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Positioning\">Positioning</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Multiple-column_Layout\">Multiple-column layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design\">Responsive design</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Media_queries\">Beginner's guide to media queries</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Legacy_Layout_Methods\">Legacy layout methods</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Supporting_Older_Browsers\">Supporting older browsers</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Fundamental_Layout_Comprehension\">Fundamental layout comprehension</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/JavaScript\">JavaScript — Dynamic client-side scripting</a></li><li><details><summary>JavaScript first steps</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps\">JavaScript first steps</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/What_is_JavaScript\">What is JavaScript?</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/A_first_splash\">A first splash into JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/What_went_wrong\">What went wrong? Troubleshooting JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Variables\">Storing the information you need — Variables</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Math\">Basic math in JavaScript — numbers and operators</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Strings\">Handling text — strings in JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods\">Useful string methods</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Arrays\">Arrays</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator\">Silly story generator</a></li></ol></details></li><li><details><summary>JavaScript building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks\">JavaScript building blocks</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/conditionals\">Making decisions in your code — conditionals</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Looping_code\">Looping code</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Functions\">Functions — reusable blocks of code</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Build_your_own_function\">Build your own function</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Return_values\">Function return values</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Events\">Introduction to events</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Event_bubbling\">Event bubbling</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Image_gallery\">Image gallery</a></li></ol></details></li><li><details><summary>Introducing JavaScript objects</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Objects\">Introducing JavaScript objects</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Basics\">JavaScript object basics</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object_prototypes\">Object prototypes</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object-oriented_programming\">Object-oriented programming</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Classes_in_JavaScript\">Classes in JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/JSON\">Working with JSON</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object_building_practice\">Object building practice</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features\">Adding features to our bouncing balls demo</a></li></ol></details></li><li><details><summary>Asynchronous JavaScript</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous\">Asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Introducing\">Introducing asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Promises\">How to use promises</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Implementing_a_promise-based_API\">How to implement a promise-based API</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Introducing_workers\">Introducing workers</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Sequencing_animations\">Sequencing animations</a></li></ol></details></li><li><details><summary>Client-side web APIs</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs\">Client-side web APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introduction\">Introduction to web APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents\">Manipulating documents</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Fetching_data\">Fetching data from the server</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Third_party_APIs\">Third-party APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Drawing_graphics\">Drawing graphics</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs\">Video and Audio APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Client-side_storage\">Client-side storage</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Forms\">Web forms — Working with user data</a></li><li><details><summary>Web form building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/Forms\">Web form building blocks</a></li><li><a href=\"/en-US/docs/Learn/Forms/Your_first_form\">Your first form</a></li><li><a href=\"/en-US/docs/Learn/Forms/How_to_structure_a_web_form\">How to structure a web form</a></li><li><a href=\"/en-US/docs/Learn/Forms/Basic_native_form_controls\">Basic native form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/HTML5_input_types\">The HTML5 input types</a></li><li><a href=\"/en-US/docs/Learn/Forms/Other_form_controls\">Other form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/Styling_web_forms\">Styling web forms</a></li><li><a href=\"/en-US/docs/Learn/Forms/Advanced_form_styling\">Advanced form styling</a></li><li><a href=\"/en-US/docs/Learn/Forms/UI_pseudo-classes\">UI pseudo-classes</a></li><li><a href=\"/en-US/docs/Learn/Forms/Form_validation\">Client-side form validation</a></li><li><a href=\"/en-US/docs/Learn/Forms/Sending_and_retrieving_form_data\">Sending form data</a></li></ol></details></li><li><details><summary>Advanced web form techniques</summary><ol><li><a href=\"/en-US/docs/Learn/Forms/How_to_build_custom_form_controls\">How to build custom form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript\">Sending forms through JavaScript</a></li><li><a href=\"/en-US/docs/Learn/Forms/Property_compatibility_table_for_form_controls\">CSS property compatibility table for form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/HTML_forms_in_legacy_browsers\">HTML forms in legacy browsers</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Accessibility\">Accessibility — Make the web usable by everyone</a></li><li><details><summary>Accessibility guides</summary><ol><li><a href=\"/en-US/docs/Learn/Accessibility\">Accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/What_is_accessibility\">What is accessibility?</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/HTML\">HTML: A good basis for accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/CSS_and_JavaScript\">CSS and JavaScript accessibility best practices</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/WAI-ARIA_basics\">WAI-ARIA basics</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Multimedia\">Accessible multimedia</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Mobile\">Mobile accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Accessibility_troubleshooting\">Assessment: Accessibility troubleshooting</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Performance\">Performance — Making websites fast and responsive</a></li><li><details><summary>Performance guides</summary><ol><li><a href=\"/en-US/docs/Learn/Performance\">Web performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/why_web_performance\">The \"why\" of web performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/What_is_web_performance\">What is web performance?</a></li><li><a href=\"/en-US/docs/Learn/Performance/Perceived_performance\">Perceived performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/Measuring_performance\">Measuring performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/Multimedia\">Multimedia: Images</a></li><li><a href=\"/en-US/docs/Learn/Performance/video\">Multimedia: video</a></li><li><a href=\"/en-US/docs/Learn/Performance/JavaScript\">JavaScript performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/HTML\">HTML performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/CSS\">CSS performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/business_case_for_performance\">The business case for web performance</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/MathML\">MathML — Writing mathematics with MathML</a></li><li><details><summary>MathML first steps</summary><ol><li><a href=\"/en-US/docs/Learn/MathML/First_steps\">MathML first steps</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Getting_started\">Getting started with MathML</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Text_containers\">MathML Text Containers</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Fractions_and_roots\">MathML fractions and roots</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Scripts\">MathML scripted elements</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Tables\">MathML tables</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Three_famous_mathematical_formulas\">Three famous mathematical formulas</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/../Games\">Games — Developing games for the web</a></li><li><details><summary>Guides and tutorials</summary><ol><li><a href=\"/en-US/docs/Games/Introduction\">Introduction to game development for the Web</a></li><li><a href=\"/en-US/docs/Games/Techniques\">Techniques for game development</a></li><li><a href=\"/en-US/docs/Games/Tutorials\">Tutorials</a></li><li><a href=\"/en-US/docs/Games/Publishing_games\">Publishing games</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Tools_and_testing\">Tools and testing</a></li><li><details><summary>Client-side web development tools</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools\">Understanding client-side web development tools</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Overview\">Client-side tooling overview</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Command_line\">Command line crash course</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Package_management\">Package management basics</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Introducing_complete_toolchain\">Introducing a complete toolchain</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Deployment\">Deploying our app</a></li></ol></details></li><li><details><summary>Introduction to client-side frameworks</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Introduction\">Introduction to client-side frameworks</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Main_features\">Framework main features</a></li></ol></details></li><li><details><summary>React</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_getting_started\">Getting started with React</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_todo_list_beginning\">Beginning our React todo list</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_components\">Componentizing our React app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_events_state\">React interactivity: Events and state</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_filtering_conditional_rendering\">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_accessibility\">Accessibility in React</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_resources\">React resources</a></li></ol></details></li><li><details><summary>Ember</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_getting_started\">Getting started with Ember</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_structure_componentization\">Ember app structure and componentization</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_interactivity_events_state\">Ember interactivity: Events, classes and state</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_conditional_footer\">Ember Interactivity: Footer functionality, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_routing\">Routing in Ember</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_resources\">Ember resources and troubleshooting</a></li></ol></details></li><li><details><summary>Vue</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_getting_started\">Getting started with Vue</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_first_component\">Creating our first Vue component</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_rendering_lists\">Rendering a list of Vue components</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_methods_events_models\">Adding a new todo form: Vue events, methods, and models</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_styling\">Styling Vue components with CSS</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_computed_properties\">Using Vue computed properties</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_conditional_rendering\">Vue conditional rendering: editing existing todos</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_refs_focus_management\">Vue refs and lifecycle methods for focus management</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_resources\">Vue resources</a></li></ol></details></li><li><details><summary>Svelte</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_getting_started\">Getting started with Svelte</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_Todo_list_beginning\">Starting our Svelte to-do list app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_variables_props\">Dynamic behavior in Svelte: working with variables and props</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_components\">Componentizing our Svelte app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_reactivity_lifecycle_accessibility\">Advanced Svelte: Reactivity, lifecycle, accessibility</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_stores\">Working with Svelte stores</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_TypeScript\">TypeScript support in Svelte</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_deployment_next\">Deployment and next steps</a></li></ol></details></li><li><details><summary>Angular</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_getting_started\">Getting started with Angular</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_todo_list_beginning\">Beginning our Angular todo list app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_styling\">Styling our Angular app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_item_component\">Creating an item component</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_filtering\">Filtering our to-do items</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_building\">Building Angular applications and further resources</a></li></ol></details></li><li><details><summary>Git and GitHub</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/GitHub\">Git and GitHub</a></li></ol></details></li><li><details><summary>Cross browser testing</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing\">Cross browser testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Introduction\">Introduction to cross-browser testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Testing_strategies\">Strategies for carrying out testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/HTML_and_CSS\">Handling common HTML and CSS problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/JavaScript\">Handling common JavaScript problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility\">Handling common accessibility problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Feature_detection\">Implementing feature detection</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Automated_testing\">Introduction to automated testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Your_own_automation_environment\">Setting up your own test automation environment</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Server-side\">Server-side website programming</a></li><li><details><summary>First steps</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/First_steps\">Server-side website programming first steps</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Introduction\">Introduction to the server side</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Client-Server_overview\">Client-Server Overview</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Web_frameworks\">Server-side web frameworks</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Website_security\">Website security</a></li></ol></details></li><li><details><summary>Django web framework (Python)</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/Django\">Django Web Framework (Python)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Introduction\">Django introduction</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/development_environment\">Setting up a Django development environment</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Tutorial_local_library_website\">Django Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/skeleton_website\">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Models\">Django Tutorial Part 3: Using models</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Admin_site\">Django Tutorial Part 4: Django admin site</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Home_page\">Django Tutorial Part 5: Creating our home page</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Generic_views\">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Sessions\">Django Tutorial Part 7: Sessions framework</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Authentication\">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Forms\">Django Tutorial Part 9: Working with forms</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Testing\">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Deployment\">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/web_application_security\">Django web application security</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/django_assessment_blog\">Assessment: DIY Django mini blog</a></li></ol></details></li><li><details><summary>Express Web Framework (Node.js/JavaScript)</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs\">Express web framework (Node.js/JavaScript)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Introduction\">Express/Node introduction</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/development_environment\">Setting up a Node development environment</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Tutorial_local_library_website\">Express Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/skeleton_website\">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/mongoose\">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/routes\">Express Tutorial Part 4: Routes and controllers</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Displaying_data\">Express Tutorial Part 5: Displaying library data</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/forms\">Express Tutorial Part 6: Working with forms</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/deployment\">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Common_questions\">Further resources</a></li><li><details><summary>Common questions</summary><ol><li><a href=\"/en-US/docs/Learn/Common_questions\">Common questions</a></li><li><a href=\"/en-US/docs/Learn/HTML/Howto\">Use HTML to solve common problems</a></li><li><a href=\"/en-US/docs/Learn/CSS/Howto\">Use CSS to solve common problems</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Howto\">Solve common problems in your JavaScript code</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Web_mechanics\">Web mechanics</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Tools_and_setup\">Tools and setup</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Design_and_accessibility\">Design and accessibility</a></li></ol></details></li></ol>","sidebarMacro":"LearnSidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<ul class=\"prev-next\">\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure\"><span class=\"button-wrap\"> Previous </span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML\"><span class=\"button-wrap\"> Overview: Introduction to HTML</span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter\"><span class=\"button-wrap\"> Next </span></a></li>\n</ul>\n<p>Writing HTML is fine, but what if something goes wrong, and you can't work out where the error in the code is? This article will introduce you to some tools that can help you find and fix errors in HTML.</p>\n<figure class=\"table-container\"><table>\n <tbody>\n <tr>\n <th scope=\"row\">Prerequisites:</th>\n <td>\n HTML familiarity, as covered in, for example, <a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started\">Getting started with HTML</a>,\n <a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals\">HTML text fundamentals</a>, and\n <a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks\">Creating hyperlinks</a>.\n </td>\n </tr>\n <tr>\n <th scope=\"row\">Objective:</th>\n <td>Learn the basics of using debugging tools to find problems in HTML.</td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"debugging_isnt_scary","title":"Debugging isn't scary","isH3":false,"content":"<p>When writing code of some kind, everything is usually fine, until that dreaded moment when an error occurs — you've done something wrong, so your code doesn't work — either not at all, or not quite how you wanted it to. For example, the following shows an error reported when trying to <a href=\"/en-US/docs/Glossary/Compile\">compile</a> a simple program written in the <a href=\"https://www.rust-lang.org/\" class=\"external\" target=\"_blank\">Rust</a> language.</p>\n<p>\n <img src=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/error-message.png\" alt=\"A console window showing the result of trying to compile a rust program with a missing quote around a string in a print statement. The error message reported is error: unterminated double quote string.\" width=\"711\" height=\"520\" loading=\"lazy\">\n</p>\n<p>Here, the error message is relatively easy to understand — \"unterminated double quote string\". If you look at the listing, you can probably see how <code>println!(Hello, world!\");</code> might logically be missing a double quote. However, error messages can quickly get more complicated and less easy to interpret as programs get bigger, and even simple cases can look a little intimidating to someone who doesn't know anything about Rust.</p>\n<p>Debugging doesn't have to be scary though — the key to being comfortable with writing and debugging any programming language or code is familiarity with both the language and the tools.</p>"}},{"type":"prose","value":{"id":"html_and_debugging","title":"HTML and debugging","isH3":false,"content":"<p>HTML is not as complicated to understand as Rust. HTML is not compiled into a different form before the browser parses it and shows the result (it is <em>interpreted</em>, not <em>compiled</em>). And HTML's <a href=\"/en-US/docs/Glossary/Element\">element</a> syntax is arguably a lot easier to understand than a \"real programming language\" like Rust, <a href=\"/en-US/docs/Glossary/JavaScript\">JavaScript</a>, or <a href=\"/en-US/docs/Glossary/Python\">Python</a>. The way that browsers parse HTML is a lot more <strong>permissive</strong> than how programming languages are run, which is both a good and a bad thing.</p>"}},{"type":"prose","value":{"id":"permissive_code","title":"Permissive code","isH3":true,"content":"<p>So what do we mean by permissive? Well, generally when you do something wrong in code, there are two main types of error that you'll come across:</p>\n<ul>\n <li><strong>Syntax errors</strong>: These are spelling or punctuation errors in your code that actually cause the program not to run, like the Rust error shown above. These are usually easy to fix as long as you are familiar with the language's syntax and know what the error messages mean.</li>\n <li><strong>Logic errors</strong>: These are errors where the syntax is actually correct, but the code is not what you intended it to be, meaning that the program runs incorrectly. These are often harder to fix than syntax errors, as there isn't an error message to direct you to the source of the error.</li>\n</ul>\n<p>HTML itself doesn't suffer from syntax errors because browsers parse it permissively, meaning that the page still displays even if there are syntax errors. Browsers have built-in rules to state how to interpret incorrectly written markup, so you'll get something running, even if it is not what you expected. This, of course, can still be a problem!</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> HTML is parsed permissively because when the web was first created, it was decided that allowing people to get their content published was more important than making sure the syntax was absolutely correct. The web would probably not be as popular as it is today, if it had been more strict from the very beginning.</p>\n</div>"}},{"type":"prose","value":{"id":"active_learning_studying_permissive_code","title":"Active learning: Studying permissive code","isH3":true,"content":"<p>It's time to study the permissive nature of HTML code.</p>\n<ol>\n <li>\n <p>First, download our <a href=\"https://github.com/mdn/learning-area/blob/main/html/introduction-to-html/debugging-html/debug-example.html\" class=\"external\" target=\"_blank\">debug-example demo</a> and save it locally. This demo is deliberately written with some built-in errors for us to explore (the HTML markup is said to be <strong>badly-formed</strong>, as opposed to <strong>well-formed</strong>).</p>\n </li>\n <li>\n <p>Next, open it in a browser. You will see something like this:\n <img src=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/badly-formed-html.png\" alt=\"A simple HTML document with a title of HTML debugging examples, and some information about common HTML errors, such as unclosed elements, badly nested elements, and unclosed attributes. \" width=\"626\" height=\"498\" loading=\"lazy\">\n </p>\n </li>\n <li>\n <p>This immediately doesn't look great; let's look at the source code to see if we can work out why (only the body contents are shown):</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><h1>HTML debugging examples</h1>\n\n<p>What causes errors in HTML?\n\n<ul>\n <li>Unclosed elements: If an element is <strong>not closed properly,\n then its effect can spread to areas you didn't intend\n\n <li>Badly nested elements: Nesting elements properly is also very important\n for code behaving correctly. <strong>strong <em>strong emphasized?</strong>\n what is this?</em>\n\n <li>Unclosed attributes: Another common source of HTML problems. Let's\n look at an example: <a href=\"https://www.mozilla.org/>link to Mozilla\n homepage</a>\n</ul>\n</code></pre></div>\n </li>\n <li>\n <p>Let's review the problems:</p>\n <ul>\n <li>The <a href=\"/en-US/docs/Web/HTML/Element/p\">paragraph</a> and <a href=\"/en-US/docs/Web/HTML/Element/li\">list item</a> elements have no closing tags. Looking at the image above, this doesn't seem to have affected the markup rendering too badly, as it is easy to infer where one element should end and another should begin.</li>\n <li>The first <a href=\"/en-US/docs/Web/HTML/Element/strong\"><code><strong></code></a> element has no closing tag. This is a bit more problematic, as it isn't easy to tell where the element is supposed to end. In fact, the whole of the rest of the text has been strongly emphasized.</li>\n <li>This section is badly nested: <code><strong>strong <em>strong emphasized?</strong> what is this?</em></code>. It is not easy to tell how this has been interpreted because of the previous problem.</li>\n <li>The <a href=\"/en-US/docs/Web/HTML/Element/a#href\"><code>href</code></a> attribute value is missing a closing double quote. This seems to have caused the biggest problem — the link has not rendered at all.</li>\n </ul>\n </li>\n <li>\n <p>Now let's look at the markup the browser has rendered, as opposed to the markup in the source code. To do this, we can use the browser developer tools. If you are not familiar with how to use your browser's developer tools, take a few minutes to review <a href=\"/en-US/docs/Learn/Common_questions/Tools_and_setup/What_are_browser_developer_tools\">Discover browser developer tools</a>.</p>\n </li>\n <li>\n <p>In the DOM inspector, you can see what the rendered markup looks like: \n <img src=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/html-inspector.png\" alt=\"The HTML inspector in Firefox, with our example's paragraph highlighted, showing the text "What causes errors in HTML?" Here you can see that the paragraph element has been closed by the browser.\" width=\"851\" height=\"715\" loading=\"lazy\">\n </p>\n </li>\n <li>\n <p>Using the DOM inspector, let's explore our code in detail to see how the browser has tried to fix our HTML errors (we did the review in Firefox; other modern browsers <em>should</em> give the same result):</p>\n <ul>\n <li>\n <p>The paragraphs and list items have been given closing tags.</p>\n </li>\n <li>\n <p>It isn't clear where the first <code><strong></code> element should be closed, so the browser has wrapped each separate block of text with its own strong tag, right down to the bottom of the document!</p>\n </li>\n <li>\n <p>The incorrect nesting has been fixed by the browser as shown here:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><strong>\n strong\n <em>strong emphasized?</em>\n</strong>\n<em> what is this?</em>\n</code></pre></div>\n </li>\n <li>\n <p>The link with the missing double quote has been deleted altogether. The last list item looks like this:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><li>\n <strong>\n Unclosed attributes: Another common source of HTML problems. Let's look\n at an example:\n </strong>\n</li>\n</code></pre></div>\n </li>\n </ul>\n </li>\n</ol>"}},{"type":"prose","value":{"id":"html_validation","title":"HTML validation","isH3":true,"content":"<p>So you can see from the above example that you really want to make sure your HTML is well-formed! But how? In a small example like the one seen above, it is easy to search through the lines and find the errors, but what about a huge, complex HTML document?</p>\n<p>The best strategy is to start by running your HTML page through the <a href=\"https://validator.w3.org/\" class=\"external\" target=\"_blank\">Markup Validation Service</a> — created and maintained by the W3C, the organization that looks after the specifications that define HTML, CSS, and other web technologies. This webpage takes an HTML document as an input, goes through it, and gives you a report to tell you what is wrong with your HTML.</p>\n<p>\n <img src=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/validator.png\" alt=\"The HTML validator homepage\" width=\"1105\" height=\"776\" loading=\"lazy\">\n</p>\n<p>To specify the HTML to validate, you can provide a web address, upload an HTML file, or directly input some HTML code.</p>"}},{"type":"prose","value":{"id":"active_learning_validating_an_html_document","title":"Active learning: Validating an HTML document","isH3":true,"content":"<p>Let's try this with our <a href=\"https://github.com/mdn/learning-area/blob/main/html/introduction-to-html/debugging-html/debug-example.html\" class=\"external\" target=\"_blank\">sample document</a>.</p>\n<ol>\n <li>First, load the <a href=\"https://validator.w3.org/\" class=\"external\" target=\"_blank\">Markup Validation Service</a> in one browser tab, if it isn't already open.</li>\n <li>Switch to the <a href=\"https://validator.w3.org/#validate_by_input\" class=\"external\" target=\"_blank\">Validate by Direct Input</a> tab.</li>\n <li>Copy all of the sample document's code (not just the body) and paste it into the large text area shown in the Markup Validation Service.</li>\n <li>Press the <em>Check</em> button.</li>\n</ol>\n<p>This should give you a list of errors and other information.</p>\n<p>\n <img src=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/validation-results.png\" alt=\"A list of HTML validation results from the W3C markup validation service\" width=\"603\" height=\"535\" loading=\"lazy\">\n</p>\n<h4 id=\"interpreting_the_error_messages\">Interpreting the error messages</h4>\n<p>The error messages are usually helpful, but sometimes they are not so helpful; with a bit of practice you can work out how to interpret these to fix your code. Let's go through the error messages and see what they mean. You'll see that each message comes with a line and column number to help you to locate the error easily.</p>\n<ul>\n <li>\n <p>\"End tag <code>li</code> implied, but there were open elements\" (2 instances): These messages indicate that an element is open that should be closed. The ending tag is implied, but not actually there. The line/column information points to the first line after the line where the closing tag should really be, but this is a good enough clue to see what is wrong.</p>\n </li>\n <li>\n <p>\"Unclosed element <code>strong</code>\": This is really easy to understand — a <a href=\"/en-US/docs/Web/HTML/Element/strong\"><code><strong></code></a> element is unclosed, and the line/column information points right to where it is.</p>\n </li>\n <li>\n <p>\"End tag <code>strong</code> violates nesting rules\": This points out the incorrectly nested elements, and the line/column information points out where they are.</p>\n </li>\n <li>\n <p>\"End of file reached when inside an attribute value. Ignoring tag\": This one is rather cryptic; it refers to the fact that there is an attribute value not properly formed somewhere, possibly near the end of the file because the end of the file appears inside the attribute value. The fact that the browser doesn't render the link should give us a good clue as to what element is at fault.</p>\n </li>\n <li>\n <p>\"End of file seen and there were open elements\": This is a bit ambiguous, but basically refers to the fact there are open elements that need to be properly closed. The line numbers point to the last few lines of the file, and this error message comes with a line of code that points out an example of an open element:</p>\n <pre class=\"brush: plain notranslate\">example: <a href=\"https://www.mozilla.org/>link to Mozilla homepage</a> ↩ </ul>↩ </body>↩</html>\n</pre>\n <div class=\"notecard note\">\n <p><strong>Note:</strong> An attribute missing a closing quote can result in an open element because the rest of the document is interpreted as the attribute's content.</p>\n </div>\n </li>\n <li>\n <p>\"Unclosed element <code>ul</code>\": This is not very helpful, as the <a href=\"/en-US/docs/Web/HTML/Element/ul\"><code><ul></code></a> element <em>is</em> closed correctly. This error comes up because the <a href=\"/en-US/docs/Web/HTML/Element/a\"><code><a></code></a> element is not closed, due to the missing closing quote mark.</p>\n </li>\n</ul>\n<p>If you can't work out what every error message means, don't worry about it — a good idea is to try fixing a few errors at a time. Then try revalidating your HTML to show what errors are left. Sometimes fixing an earlier error will also get rid of other error messages — several errors can often be caused by a single problem, in a domino effect.</p>\n<p>You will know when all your errors are fixed when you see the following banner in your output:</p>\n<p>\n <img src=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML/valid-html-banner.png\" alt=\"Banner that reads "The document validates according to the specified schema(s) and to additional constraints checked by the validator."\" width=\"934\" height=\"46\" loading=\"lazy\">\n</p>"}},{"type":"prose","value":{"id":"summary","title":"Summary","isH3":false,"content":"<p>So there we have it, an introduction to debugging HTML, which should give you some useful skills to count on when you start to debug CSS, JavaScript, and other types of code later on in your career. This also marks the end of the Introduction to HTML module learning articles — now you can go on to testing yourself with our assessments: the first one is linked below.</p><ul class=\"prev-next\">\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure\"><span class=\"button-wrap\"> Previous </span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML\"><span class=\"button-wrap\"> Overview: Introduction to HTML</span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter\"><span class=\"button-wrap\"> Next </span></a></li>\n</ul>"}}],"toc":[{"text":"Debugging isn't scary","id":"debugging_isnt_scary"},{"text":"HTML and debugging","id":"html_and_debugging"},{"text":"Summary","id":"summary"}],"summary":"So there we have it, an introduction to debugging HTML, which should give you some useful skills to count on when you start to debug CSS, JavaScript, and other types of code later on in your career. This also marks the end of the Introduction to HTML module learning articles — now you can go on to testing yourself with our assessments: the first one is linked below.","popularity":0.0098,"modified":"2024-07-25T19:35:50.000Z","other_translations":[{"locale":"de","title":"Debugging HTML","native":"Deutsch"},{"locale":"es","title":"Depurar el HTML","native":"Español"},{"locale":"fr","title":"Déboguer de l'HTML","native":"Français"},{"locale":"ja","title":"HTML のデバッグ","native":"日本語"},{"locale":"pt-BR","title":"Debugging HTML","native":"Português (do Brasil)"},{"locale":"ru","title":"Отладка HTML","native":"Русский"},{"locale":"zh-CN","title":"HTML 调试","native":"中文 (简体)"}],"pageType":"learn-module-chapter","source":{"folder":"en-us/learn/html/introduction_to_html/debugging_html","github_url":"https://github.com/mdn/content/blob/main/files/en-us/learn/html/introduction_to_html/debugging_html/index.md","last_commit_url":"https://github.com/mdn/content/commit/76c1e86a6bf1fd58aa6b0e627842a3c1161add28","filename":"index.md"},"short_title":"Debugging HTML","parents":[{"uri":"/en-US/docs/Learn","title":"Guides"},{"uri":"/en-US/docs/Learn/HTML","title":"HTML"},{"uri":"/en-US/docs/Learn/HTML/Introduction_to_HTML","title":"Introduction to HTML"},{"uri":"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML","title":"Debugging HTML"}],"pageTitle":"Debugging HTML - Learn web development | MDN","noIndexing":false}}</script></body></html>