Ha, ha.
A nice little joke, yet one with a grain of truth in it.

It certainly makes as much sense for there to be an XHTML2 Grammar 
Module as there does an XHTML2 Computing Module, Indeed, we've already 
had several requested elements that would fit in such a module, one of 
which, nr, is still under consideration.

Here follows a semi-serious proposal for a Grammar Module

<sentence>
<clause>
<subject> or <subj>
<predicate> or <pred>
<nounp> or <np> (noun phrase)
<verbp> or <vp> (verb phrase)
<prepp> or <pp> (prepositional phrase)
<noun> or <n>
<pronoun> or <pron>
<verb> or <v>
<adjective> or <adj>
<adverb> or <adv>
<preposition> or <prep>
<conjunction> or <conj>
<interjection> or <interj>
<determiner> or <det>

Each of the parts of the speech would of course also need to have 
attributes defined so as to allow for even finer grained information to 
be provided for those who really feel the need to include it. (The 
proposed nr element could be handled as <adj role="number"> in such a 
module.

<sentence>
 <conj>However</conj>,
 <clause>
  <clause mood="subjunctive">
   <conj>if</conj>
   <subj><np><pron person="2">you</pron></np></subj>
   <pred tense="present">
    <v>think</v>
    <np>
     <pron>that</pron>
     <clause>
      <subj><np><pron person="1" number="sing">I</pron></np></subj>
      <pred tense="present">
       <v role="aux">would</v>
       <v role="main">want</v>
       <np>
        <adj>every</adj>
        <n>sentence</n>
        <pp role="adj">
         <p>in</p>
         <n><abbr title="XML HTML Version 2.0">XHTML2</abbr></n>
        </pp>
        <vp role="adj">
         <v>marked</v>
         <np>
          <adj>this</adj>
          
<n>way</n></np></vp></np></pred></clause></np></pred></clause>,
  <clause>
   <conj>then</conj>
   <subj><np><pron number="2">you</pron></np></subj>
   <pred tense="present">
    <v>are</v>
    <adj>crazy</adj></pred></clause></clause>!
</sentence>

Rather, even if something like this were included in XHTML2, (which I 
am not in favor of, just as I am not in favor of the elements that 
would be in the proposed Computing Module.) I would expect it to be 
used only when the author considered marking up the grammar to be 
important in conveying his meaning.