Editing Markup language (section)

====XHTML====
{{Main|XHTML}}
From January 2000 until HTML 5 was released, all [[W3C Recommendation]]s for HTML have been based on XML, using the abbreviation [[XHTML]] ('''Ex'''tensible '''H'''yper'''T'''ext '''M'''arkup '''L'''anguage). The language specification requires that XHTML Web documents be ''well-formed'' XML documents. This allows for more rigorous and robust documents, by avoiding many syntax errors which historically led to incompatible browser behaviors, while still using document components that are familiar with HTML.

One of the most noticeable differences between HTML and XHTML is the rule that ''all tags must be closed'': empty HTML tags such as <code><nowiki><br></nowiki></code> must either be ''closed'' with a regular end-tag, or replaced by a special form: {{nowrap|<code><nowiki><br /></nowiki></code>}} (the space before the '<code><nowiki>/</nowiki></code>' on the end tag is optional, but frequently used because it enables some pre-XML Web browsers, and SGML parsers, to accept the tag). Another difference is that all [[HTML#Attributes|attribute]] values in tags must be quoted. Both these differences are commonly criticized as verbose but also praised because they make it far easier to detect, localize, and repair errors. Finally, all tag and attribute names within the XHTML namespace must be lowercase to be valid. HTML, on the other hand, was case-insensitive.