Target DTD for PEAR manual?

Hi,

I'm going to work a little bit on PhD_PEAR package to fix several obvious 
problems with generated documentation (broken tables due to missing colspan / 
rowspan, missing id attributes so #links don't work, etc).

Before I start this, I wanted to consult a bit about what DTD should be used for 
generated docs.

I tried validating a page [1] from QuickForm2 docs with W3C validator [2]:
  * If HTML5 doctype is used (it is currently used on the website) we get 97 errors
  * If XHTML 1.0 Strict is forced, we only get 4 errors

The XHTML errors deal with block elements appearing in inline contexts and vice 
versa. HTML5 errors deal with the same but also with obsolete <tt> tag and 
<tr>'s valign attributes (it will require a generous amount of CSS changes to 
fix these).

So, a question
  1) Why are we using HTML5 doctype in the first place?
  2) Should I try to fix output of PhD_PEAR to produce valid HTML5? Or valid XHTML?

BTW, right now chunked-XHTML format in PhD_PEAR uses XHTML 1.0 transitional and 
big-XHTML uses HTML 4.01 transitional (these are the formats for downloaded 
documentation).

[1] http://pear.php.net/manual/en/package.html.html-quickform2.rules.php
[2] http://validator.w3.org