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class="document-toc-link" href="#recommendations">Recommendations</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></div><div class="sidebar-body"><ol><li class="section"><a href="/en-US/docs/Web/XML">XML</a></li><li class="toggle"><details open=""><summary><a href="/en-US/docs/Web/XML/Guides">XML Guides</a></summary><ol><li><em><a href="/en-US/docs/Web/XML/Guides/XML_introduction" aria-current="page">XML introduction</a></em></li><li><a href="/en-US/docs/Web/XML/Guides/Parsing_and_serializing_XML">Parsing and serializing XML</a></li><li><a href="/en-US/docs/Web/XML/Guides/OpenSearch">OpenSearch description format</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Web/XML/XPath">XPath</a></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/XPath/Guides">XPath Guides</a></summary><ol><li><a href="/en-US/docs/Web/XML/XPath/Guides/Snippets">XPath snippets</a></li><li><a href="/en-US/docs/Web/XML/XPath/Guides/Comparison_with_CSS_selectors">Comparison of CSS Selectors and XPath</a></li><li><a href="/en-US/docs/Web/XML/XPath/Guides/Introduction_to_using_XPath_in_JavaScript">Introduction to using XPath in JavaScript</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/XPath/Reference/Functions">XPath Functions</a></summary><ol><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/boolean">boolean</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/ceiling">ceiling</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/choose">choose</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/concat">concat</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/contains">contains</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/count">count</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/current">current</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/document">document</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/element-available">element-available</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/false">false</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/floor">floor</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/format-number">format-number</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/function-available">function-available</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/generate-id">generate-id</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/id">id</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/key">key</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/lang">lang</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/last">last</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/local-name">local-name</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/name">name</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/namespace-uri">namespace-uri</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/normalize-space">normalize-space</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/not">not</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/number">number</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/position">position</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/round">round</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/starts-with">starts-with</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/string">string</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/string-length">string-length</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/substring">substring</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/substring-after">substring-after</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/substring-before">substring-before</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/sum">sum</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/system-property">system-property</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/translate">translate</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/true">true</a></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Functions/unparsed-entity-url">unparsed-entity-url</a></li></ol></details></li><li><a href="/en-US/docs/Web/XML/XPath/Reference/Axes">Xpath axes</a></li><li class="section"><a href="/en-US/docs/Web/XML/XSLT">XSLT</a></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/XSLT/Guides">XSLT Guides</a></summary><ol><li><a href="/en-US/docs/Web/XML/XSLT/Guides/Transforming_XML_with_XSLT">Transforming XML with XSLT</a></li><li><a href="/en-US/docs/Web/XML/XSLT/Guides/PI_Parameters">PI Parameters</a></li><li><a href="/en-US/docs/Web/XML/XSLT/Guides/Common_errors">Common XSLT Errors</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/XSLT/Reference/Element">XSLT Elements</a></summary><ol><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/apply-imports"><xsl:apply-imports></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/apply-templates"><xsl:apply-templates></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/attribute-set"><xsl:attribute-set></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/attribute"><xsl:attribute></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/call-template"><xsl:call-template></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/choose"><xsl:choose></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/comment"><xsl:comment></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/copy-of"><xsl:copy-of></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/copy"><xsl:copy></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/decimal-format"><xsl:decimal-format></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/element"><xsl:element></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/fallback"><xsl:fallback></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/for-each"><xsl:for-each></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/if"><xsl:if></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/import"><xsl:import></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/include"><xsl:include></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/key"><xsl:key></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/message"><xsl:message></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/namespace-alias"><xsl:namespace-alias></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/number"><xsl:number></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/otherwise"><xsl:otherwise></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/output"><xsl:output></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/param"><xsl:param></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/preserve-space"><xsl:preserve-space></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/processing-instruction"><xsl:processing-instruction></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/sort"><xsl:sort></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/strip-space"><xsl:strip-space></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/stylesheet"><xsl:stylesheet></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/template"><xsl:template></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/text"><xsl:text></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/transform"><xsl:transform></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/value-of"><xsl:value-of></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/variable"><xsl:variable></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/when"><xsl:when></a></li><li><a href="/en-US/docs/Web/XML/XSLT/Reference/Element/with-param"><xsl:with-param></a></li></ol></details></li><li class="section"><a href="/en-US/docs/Web/XML/EXSLT">EXSLT</a></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/EXSLT/Reference/exsl">EXSLT exsl</a></summary><ol><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/exsl/node-set">exsl:node-set()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/exsl/object-type">exsl:object-type()</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/EXSLT/Reference/math">EXSLT math</a></summary><ol><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/math/highest">math:highest()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/math/lowest">math:lowest()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/math/max">math:max()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/math/min">math:min()</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/EXSLT/Reference/regexp">EXSLT regexp</a></summary><ol><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/regexp/match">regexp:match()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/regexp/replace">regexp:replace()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/regexp/test">regexp:test()</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/EXSLT/Reference/set">EXSLT set</a></summary><ol><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/set/difference">set:difference()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/set/distinct">set:distinct()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/set/has-same-node">set:has-same-node()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/set/intersection">set:intersection()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/set/leading">set:leading()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/set/trailing">set:trailing()</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Web/XML/EXSLT/Reference/str">EXSLT str</a></summary><ol><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/str/concat">str:concat()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/str/split">str:split()</a></li><li><a href="/en-US/docs/Web/XML/EXSLT/Reference/str/tokenize">str:tokenize()</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="#structure_of_an_xml_document">Structure of an XML document</a></li><li class="document-toc-item "><a class="document-toc-link" href="#correct_xml_valid_and_well-formed">"Correct" XML (valid and well-formed)</a></li><li class="document-toc-item "><a class="document-toc-link" href="#character_references">Character references</a></li><li class="document-toc-item "><a class="document-toc-link" href="#displaying_xml">Displaying XML</a></li><li class="document-toc-item "><a class="document-toc-link" href="#recommendations">Recommendations</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</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>XML introduction</h1></header><div class="section-content"><p>XML (Extensible Markup Language) is a markup language similar to <a href="/en-US/docs/Glossary/HTML">HTML</a>, but without predefined tags to use. Instead, you define your own tags designed specifically for your needs. This is a powerful way to store data in a format that can be stored, searched, and shared. Most importantly, since the fundamental format of XML is standardized, if you share or transmit XML across systems or platforms, either locally or over the internet, the recipient can still parse the data due to the standardized XML syntax.</p> <p>There are many languages based on XML, including <a href="/en-US/docs/Glossary/XHTML">XHTML</a>, <a href="/en-US/docs/Web/MathML">MathML</a>, <a href="/en-US/docs/Web/SVG">SVG</a>, <a href="/en-US/docs/Glossary/RSS">RSS</a>, and <a href="/en-US/docs/Glossary/RDF">RDF</a>. You can also define your own.</p></div><section aria-labelledby="structure_of_an_xml_document"><h2 id="structure_of_an_xml_document"><a href="#structure_of_an_xml_document">Structure of an XML document</a></h2><div class="section-content"><p>The whole structure of XML and XML-based languages is built on <a href="/en-US/docs/Glossary/Tag">tag</a>s.</p></div></section><section aria-labelledby="xml_declaration"><h3 id="xml_declaration"><a href="#xml_declaration">XML declaration</a></h3><div class="section-content"><p>XML - declaration is not a tag. It is used for the transmission of the meta-data of a document.</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><?xml version="1.0" encoding="UTF-8"?> </code></pre></div> <h4 id="attributes">Attributes</h4> <dl> <dt id="version"><a href="#version"><code>version</code></a></dt> <dd> <p>Used version XML in this document.</p> </dd> <dt id="encoding"><a href="#encoding"><code>encoding</code></a></dt> <dd> <p>Used encoding in this document.</p> </dd> </dl></div></section><section aria-labelledby="comments"><h3 id="comments"><a href="#comments">Comments</a></h3><div class="section-content"><div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code> </code></pre></div></div></section><section aria-labelledby="correct_xml_valid_and_well-formed"><h2 id="correct_xml_valid_and_well-formed"><a href="#correct_xml_valid_and_well-formed">"Correct" XML (valid and well-formed)</a></h2><div class="section-content"></div></section><section aria-labelledby="correct_design_rules"><h3 id="correct_design_rules"><a href="#correct_design_rules">Correct design rules</a></h3><div class="section-content"><p>For an XML document to be correct, the following conditions must be fulfilled:</p> <ul> <li>Document must be well-formed.</li> <li>Document must conform to all XML syntax rules.</li> <li>Document must conform to semantic rules, which are usually set in an XML schema or a DTD (<strong><a href="/en-US/docs/Glossary/Doctype">Document Type Definition</a>)</strong>.</li> </ul></div></section><section aria-labelledby="example"><h3 id="example"><a href="#example">Example</a></h3><div class="section-content"><div class="code-example"><div class="example-header"><span class="language-name">xml</span></div><pre class="brush: xml notranslate"><code><?xml version="1.0" encoding="UTF-8"?> <message> <warning> Hello World  </message> </code></pre></div> <p>Now let's look at a corrected version of that same document:</p> <div class="code-example"><div class="example-header"><span class="language-name">xml</span></div><pre class="brush: xml notranslate"><code><?xml version="1.0" encoding="UTF-8"?> <message> <warning> Hello World </warning> </message> </code></pre></div> <p>A document that contains an undefined tag is invalid. For example, if we never defined the <code><warning></code> tag, the document above wouldn't be valid.</p> <p>Most browsers offer a debugger that can identify poorly-formed XML documents.</p></div></section><section aria-labelledby="character_references"><h2 id="character_references"><a href="#character_references">Character references</a></h2><div class="section-content"><p>Like HTML, XML offers <a href="/en-US/docs/Glossary/Character_reference">character references</a> for referring to some special reserved characters (such as a greater than sign which is used for tags). There are five of these characters that you should know:</p> <figure class="table-container"><table> <thead> <tr> <th>Entity</th> <th>Character</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td>&lt;</td> <td><</td> <td>Less than sign</td> </tr> <tr> <td>&gt;</td> <td>></td> <td>Greater than sign</td> </tr> <tr> <td>&amp;</td> <td>&</td> <td>Ampersand</td> </tr> <tr> <td>&quot;</td> <td>"</td> <td>One double-quotation mark</td> </tr> <tr> <td>&apos;</td> <td>'</td> <td>One apostrophe (or single-quotation mark)</td> </tr> </tbody> </table></figure> <p>Even though there are only 5 declared character references, or entities, more can be added using the document's <a href="/en-US/docs/Glossary/Doctype">Document Type Definition</a>. For example, to create a new <code>&warning;</code> entity, you can do this:</p> <div class="code-example"><div class="example-header"><span class="language-name">xml</span></div><pre class="brush: xml notranslate"><code><?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE body [ <!ENTITY warning "Warning: Something bad happened... please refresh and try again."> ]> <body> <message> &warning; </message> </body> </code></pre></div> <p>You can also use numeric character references to specify special characters; for example, &#xA9; is the "©" symbol.</p></div></section><section aria-labelledby="displaying_xml"><h2 id="displaying_xml"><a href="#displaying_xml">Displaying XML</a></h2><div class="section-content"><p>XML is usually used for descriptive purposes, but there are ways to display XML data. If you don't define a specific way for the XML to be rendered, the raw XML is displayed in the browser.</p> <p>One way to style XML output is to specify <a href="/en-US/docs/Web/CSS">CSS</a> to apply to the document using the <code>xml-stylesheet</code> processing instruction.</p> <div class="code-example"><div class="example-header"><span class="language-name">xml</span></div><pre class="brush: xml notranslate"><code><?xml-stylesheet type="text/css" href="stylesheet.css"?> </code></pre></div> <p>There is also another more powerful way to display XML: the <strong>Extensible Stylesheet Language Transformations</strong> (<a href="/en-US/docs/Web/XML/XSLT">XSLT</a>) which can be used to transform XML into other languages such as HTML. This makes XML incredibly versatile.</p> <div class="code-example"><div class="example-header"><span class="language-name">xml</span></div><pre class="brush: xml notranslate"><code><?xml-stylesheet type="text/xsl" href="transform.xsl"?> </code></pre></div></div></section><section aria-labelledby="recommendations"><h2 id="recommendations"><a href="#recommendations">Recommendations</a></h2><div class="section-content"><p>This article is obviously only a very brief introduction to what XML is, with a few small examples and references to get you started. 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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/Web/XML/Guides/XML_introduction","doc":{"body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<p>XML (Extensible Markup Language) is a markup language similar to <a href=\"/en-US/docs/Glossary/HTML\">HTML</a>, but without predefined tags to use. Instead, you define your own tags designed specifically for your needs. This is a powerful way to store data in a format that can be stored, searched, and shared. Most importantly, since the fundamental format of XML is standardized, if you share or transmit XML across systems or platforms, either locally or over the internet, the recipient can still parse the data due to the standardized XML syntax.</p>\n<p>There are many languages based on XML, including <a href=\"/en-US/docs/Glossary/XHTML\">XHTML</a>, <a href=\"/en-US/docs/Web/MathML\">MathML</a>, <a href=\"/en-US/docs/Web/SVG\">SVG</a>, <a href=\"/en-US/docs/Glossary/RSS\">RSS</a>, and <a href=\"/en-US/docs/Glossary/RDF\">RDF</a>. You can also define your own.</p>"}},{"type":"prose","value":{"id":"structure_of_an_xml_document","title":"Structure of an XML document","isH3":false,"content":"<p>The whole structure of XML and XML-based languages is built on <a href=\"/en-US/docs/Glossary/Tag\">tag</a>s.</p>"}},{"type":"prose","value":{"id":"xml_declaration","title":"XML declaration","isH3":true,"content":"<p>XML - declaration is not a tag. It is used for the transmission of the meta-data of a document.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><?xml version=\"1.0\" encoding=\"UTF-8\"?>\n</code></pre></div>\n<h4 id=\"attributes\">Attributes</h4>\n<dl>\n<dt id=\"version\"><a href=\"#version\"><code>version</code></a></dt>\n<dd>\n<p>Used version XML in this document.</p>\n</dd>\n<dt id=\"encoding\"><a href=\"#encoding\"><code>encoding</code></a></dt>\n<dd>\n<p>Used encoding in this document.</p>\n</dd>\n</dl>"}},{"type":"prose","value":{"id":"comments","title":"Comments","isH3":true,"content":"<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code>\n</code></pre></div>"}},{"type":"prose","value":{"id":"correct_xml_valid_and_well-formed","title":"\"Correct\" XML (valid and well-formed)","isH3":false,"content":""}},{"type":"prose","value":{"id":"correct_design_rules","title":"Correct design rules","isH3":true,"content":"<p>For an XML document to be correct, the following conditions must be fulfilled:</p>\n<ul>\n<li>Document must be well-formed.</li>\n<li>Document must conform to all XML syntax rules.</li>\n<li>Document must conform to semantic rules, which are usually set in an XML schema or a DTD (<strong><a href=\"/en-US/docs/Glossary/Doctype\">Document Type Definition</a>)</strong>.</li>\n</ul>"}},{"type":"prose","value":{"id":"example","title":"Example","isH3":true,"content":"<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">xml</span></div><pre class=\"brush: xml notranslate\"><code><?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<message>\n <warning>\n Hello World\n \n</message>\n</code></pre></div>\n<p>Now let's look at a corrected version of that same document:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">xml</span></div><pre class=\"brush: xml notranslate\"><code><?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<message>\n <warning>\n Hello World\n </warning>\n</message>\n</code></pre></div>\n<p>A document that contains an undefined tag is invalid. For example, if we never defined the <code><warning></code> tag, the document above wouldn't be valid.</p>\n<p>Most browsers offer a debugger that can identify poorly-formed XML documents.</p>"}},{"type":"prose","value":{"id":"character_references","title":"Character references","isH3":false,"content":"<p>Like HTML, XML offers <a href=\"/en-US/docs/Glossary/Character_reference\">character references</a> for referring to some special reserved characters (such as a greater than sign which is used for tags). There are five of these characters that you should know:</p>\n<figure class=\"table-container\"><table>\n<thead>\n<tr>\n<th>Entity</th>\n<th>Character</th>\n<th>Description</th>\n</tr>\n</thead>\n<tbody>\n<tr>\n<td>&lt;</td>\n<td><</td>\n<td>Less than sign</td>\n</tr>\n<tr>\n<td>&gt;</td>\n<td>></td>\n<td>Greater than sign</td>\n</tr>\n<tr>\n<td>&amp;</td>\n<td>&</td>\n<td>Ampersand</td>\n</tr>\n<tr>\n<td>&quot;</td>\n<td>\"</td>\n<td>One double-quotation mark</td>\n</tr>\n<tr>\n<td>&apos;</td>\n<td>'</td>\n<td>One apostrophe (or single-quotation mark)</td>\n</tr>\n</tbody>\n</table></figure>\n<p>Even though there are only 5 declared character references, or entities, more can be added using the document's <a href=\"/en-US/docs/Glossary/Doctype\">Document Type Definition</a>. For example, to create a new <code>&warning;</code> entity, you can do this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">xml</span></div><pre class=\"brush: xml notranslate\"><code><?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<!DOCTYPE body [\n <!ENTITY warning \"Warning: Something bad happened... please refresh and try again.\">\n]>\n<body>\n <message> &warning; </message>\n</body>\n</code></pre></div>\n<p>You can also use numeric character references to specify special characters; for example, &#xA9; is the \"©\" symbol.</p>"}},{"type":"prose","value":{"id":"displaying_xml","title":"Displaying XML","isH3":false,"content":"<p>XML is usually used for descriptive purposes, but there are ways to display XML data. If you don't define a specific way for the XML to be rendered, the raw XML is displayed in the browser.</p>\n<p>One way to style XML output is to specify <a href=\"/en-US/docs/Web/CSS\">CSS</a> to apply to the document using the <code>xml-stylesheet</code> processing instruction.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">xml</span></div><pre class=\"brush: xml notranslate\"><code><?xml-stylesheet type=\"text/css\" href=\"stylesheet.css\"?>\n</code></pre></div>\n<p>There is also another more powerful way to display XML: the <strong>Extensible Stylesheet Language Transformations</strong> (<a href=\"/en-US/docs/Web/XML/XSLT\">XSLT</a>) which can be used to transform XML into other languages such as HTML. This makes XML incredibly versatile.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">xml</span></div><pre class=\"brush: xml notranslate\"><code><?xml-stylesheet type=\"text/xsl\" href=\"transform.xsl\"?>\n</code></pre></div>"}},{"type":"prose","value":{"id":"recommendations","title":"Recommendations","isH3":false,"content":"<p>This article is obviously only a very brief introduction to what XML is, with a few small examples and references to get you started. For more details about XML, you should look around on the Web for more in-depth articles.</p>\n<p>Learning the HyperText Markup Language (<a href=\"/en-US/docs/Web/HTML\">HTML</a>) will help you better understand XML.</p>"}},{"type":"prose","value":{"id":"see_also","title":"See also","isH3":false,"content":"<ul>\n<li><a href=\"https://www.xml.com/\" class=\"external\" target=\"_blank\">XML.com</a></li>\n<li><a href=\"https://www.w3.org/XML/\" class=\"external\" target=\"_blank\">Extensible Markup Language (XML) @ W3.org</a></li>\n<li><a href=\"https://alistapart.com/article/usingxml/\" class=\"external\" target=\"_blank\">Using XML: A List Apart</a></li>\n</ul>"}}],"isActive":true,"isMarkdown":true,"isTranslated":false,"locale":"en-US","mdn_url":"/en-US/docs/Web/XML/Guides/XML_introduction","modified":"2025-02-05T13:56:43.000Z","native":"English (US)","noIndexing":false,"other_translations":[{"locale":"de","title":"Einführung in XML","native":"Deutsch"},{"locale":"es","title":"Introducción a XML","native":"Español"},{"locale":"fr","title":"Introduction à XML","native":"Français"},{"locale":"ja","title":"XML 入門","native":"日本語"},{"locale":"ko","title":"XML 소개","native":"한국어"},{"locale":"ru","title":"XML Введение","native":"Русский"},{"locale":"zh-CN","title":"XML 简介","native":"中文 (简体)"}],"pageTitle":"XML introduction - XML: Extensible Markup Language | MDN","parents":[{"uri":"/en-US/docs/Web","title":"References"},{"uri":"/en-US/docs/Web/XML","title":"XML"},{"uri":"/en-US/docs/Web/XML/Guides","title":"Guides"},{"uri":"/en-US/docs/Web/XML/Guides/XML_introduction","title":"XML introduction"}],"popularity":null,"short_title":"XML introduction","sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Web/XML\">XML</a></li><li class=\"toggle\"><details open=\"\"><summary><a href=\"/en-US/docs/Web/XML/Guides\">XML Guides</a></summary><ol><li><em><a href=\"/en-US/docs/Web/XML/Guides/XML_introduction\" aria-current=\"page\">XML introduction</a></em></li><li><a href=\"/en-US/docs/Web/XML/Guides/Parsing_and_serializing_XML\">Parsing and serializing XML</a></li><li><a href=\"/en-US/docs/Web/XML/Guides/OpenSearch\">OpenSearch description format</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Web/XML/XPath\">XPath</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/XPath/Guides\">XPath Guides</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/XPath/Guides/Snippets\">XPath snippets</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Guides/Comparison_with_CSS_selectors\">Comparison of CSS Selectors and XPath</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Guides/Introduction_to_using_XPath_in_JavaScript\">Introduction to using XPath in JavaScript</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions\">XPath Functions</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/boolean\">boolean</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/ceiling\">ceiling</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/choose\">choose</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/concat\">concat</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/contains\">contains</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/count\">count</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/current\">current</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/document\">document</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/element-available\">element-available</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/false\">false</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/floor\">floor</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/format-number\">format-number</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/function-available\">function-available</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/generate-id\">generate-id</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/id\">id</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/key\">key</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/lang\">lang</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/last\">last</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/local-name\">local-name</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/name\">name</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/namespace-uri\">namespace-uri</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/normalize-space\">normalize-space</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/not\">not</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/number\">number</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/position\">position</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/round\">round</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/starts-with\">starts-with</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/string\">string</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/string-length\">string-length</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/substring\">substring</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/substring-after\">substring-after</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/substring-before\">substring-before</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/sum\">sum</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/system-property\">system-property</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/translate\">translate</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/true\">true</a></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Functions/unparsed-entity-url\">unparsed-entity-url</a></li></ol></details></li><li><a href=\"/en-US/docs/Web/XML/XPath/Reference/Axes\">Xpath axes</a></li><li class=\"section\"><a href=\"/en-US/docs/Web/XML/XSLT\">XSLT</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/XSLT/Guides\">XSLT Guides</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/XSLT/Guides/Transforming_XML_with_XSLT\">Transforming XML with XSLT</a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Guides/PI_Parameters\">PI Parameters</a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Guides/Common_errors\">Common XSLT Errors</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element\">XSLT Elements</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/apply-imports\"><xsl:apply-imports></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/apply-templates\"><xsl:apply-templates></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/attribute-set\"><xsl:attribute-set></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/attribute\"><xsl:attribute></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/call-template\"><xsl:call-template></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/choose\"><xsl:choose></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/comment\"><xsl:comment></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/copy-of\"><xsl:copy-of></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/copy\"><xsl:copy></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/decimal-format\"><xsl:decimal-format></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/element\"><xsl:element></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/fallback\"><xsl:fallback></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/for-each\"><xsl:for-each></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/if\"><xsl:if></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/import\"><xsl:import></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/include\"><xsl:include></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/key\"><xsl:key></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/message\"><xsl:message></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/namespace-alias\"><xsl:namespace-alias></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/number\"><xsl:number></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/otherwise\"><xsl:otherwise></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/output\"><xsl:output></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/param\"><xsl:param></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/preserve-space\"><xsl:preserve-space></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/processing-instruction\"><xsl:processing-instruction></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/sort\"><xsl:sort></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/strip-space\"><xsl:strip-space></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/stylesheet\"><xsl:stylesheet></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/template\"><xsl:template></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/text\"><xsl:text></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/transform\"><xsl:transform></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/value-of\"><xsl:value-of></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/variable\"><xsl:variable></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/when\"><xsl:when></a></li><li><a href=\"/en-US/docs/Web/XML/XSLT/Reference/Element/with-param\"><xsl:with-param></a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Web/XML/EXSLT\">EXSLT</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/exsl\">EXSLT exsl</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/exsl/node-set\">exsl:node-set()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/exsl/object-type\">exsl:object-type()</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/math\">EXSLT math</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/math/highest\">math:highest()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/math/lowest\">math:lowest()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/math/max\">math:max()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/math/min\">math:min()</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/regexp\">EXSLT regexp</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/regexp/match\">regexp:match()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/regexp/replace\">regexp:replace()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/regexp/test\">regexp:test()</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set\">EXSLT set</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set/difference\">set:difference()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set/distinct\">set:distinct()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set/has-same-node\">set:has-same-node()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set/intersection\">set:intersection()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set/leading\">set:leading()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/set/trailing\">set:trailing()</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/str\">EXSLT str</a></summary><ol><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/str/concat\">str:concat()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/str/split\">str:split()</a></li><li><a href=\"/en-US/docs/Web/XML/EXSLT/Reference/str/tokenize\">str:tokenize()</a></li></ol></details></li></ol>","sidebarMacro":"xmlsidebar","source":{"folder":"en-us/web/xml/guides/xml_introduction","github_url":"https://github.com/mdn/content/blob/main/files/en-us/web/xml/guides/xml_introduction/index.md","last_commit_url":"https://github.com/mdn/content/commit/3e1b5277c6451e7d27ab628f23fb9702947a7a7b","filename":"index.md"},"summary":"XML (Extensible Markup Language) is a markup language similar to HTML, but without predefined tags to use. Instead, you define your own tags designed specifically for your needs. This is a powerful way to store data in a format that can be stored, searched, and shared. Most importantly, since the fundamental format of XML is standardized, if you share or transmit XML across systems or platforms, either locally or over the internet, the recipient can still parse the data due to the standardized XML syntax.","title":"XML introduction","toc":[{"text":"Structure of an XML document","id":"structure_of_an_xml_document"},{"text":"\"Correct\" XML (valid and well-formed)","id":"correct_xml_valid_and_well-formed"},{"text":"Character references","id":"character_references"},{"text":"Displaying XML","id":"displaying_xml"},{"text":"Recommendations","id":"recommendations"},{"text":"See also","id":"see_also"}],"pageType":"guide"}}</script></body></html>