A very terse HTML summarizer could be specified with a table that only puts emphasized words into the keywords attribute:
HTML ELEMENT SOIF ATTRIBUTES
------------ -----------------------
<A> keywords
<B> keywords
<EM> keywords
<H1> keywords
<H2> keywords
<H3> keywords
<I> keywords
<META:CONTENT> $NAME
<STRONG> keywords
<TITLE> title,keywords
<TT> keywords
Conversely, a full-text summarizer can be easily specified with only:
HTML ELEMENT SOIF ATTRIBUTES
------------ -----------------------
<HTML> full-text
<TITLE> title,parent