PEAR standards: require XHTML 1.0?

I was just looking over the PEAR standards for the first time (very interesting!!). They're fairly good. However, in the interest of promoting standards everywhere, I would suggest PEAR include a new requirement. I feel any PEAR script echoing any HTML tags should be compliant with at least one of the XHTML 1.0 document type definitions. A simple test for this is to validate both the original document and a sample PHP-processed document using the HTML Validator at http://validator.w3.org . It's actually pretty easy to write XHTML 1.0 markup once you know how to write HTML. The two biggest things to remember are lowercase all your HTML tags and attributes, and include closing tags for everything. Attribute minimalization is prohibited -- instead of <script defer></script>, use <script defer="defer"></script>. Your requirement of <?php...?> instead of <?...?> already conforms to XML 1.0 and XHTML 1.0 in the definition of processing instructions. Opinions?