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Compile-time Errors
Why do I get a FATAL_ERROR about end tags when I use XHTML?
XHTML is not very different from HTML 4.01. However, because XHTML follows the rules of XML, it treats the characters < and & as markup, even if they reside inside a <script> block. This creates a problem when you use these characters in javascript. Although lenient browser parsers may allow these characters, to ensure your code is interpreted correctly and as you intended on all browsers, Caja requires you to escape these characters.
You can get around this conflict and make all JavaScript code compatible with XHTML by placing the JavaScript code within a CDATA section. A CDATA section XHTML starts with the characters <![CDATA[ and ends with the characters ]]>. Alternatively, you can declare your pages to be written in HTML 4.01 by setting the doctype of the page to <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">