Hi,
in function-formatting.php, around line 61:
$pee = preg_replace('!(<(?:table|caption|thead|tbody|etc. );
62;
pee = preg_replace('!(</(?:table|caption|thead|tbody|etc.);
67:
$pee = preg_replace('!\s*(</?(?:table|caption|thead|tbody|etc.);
71:
$pee = preg_replace('!\s*(</?(?:table|caption|thead|tbody|etc.);
72:
$pee = preg_replace('!(</?(?:table|thead|caption|tbody|etc.);
74:
$pee = preg_replace('!(</?(?:table|caption|thead|tbody|etc.);
than you can use <caption>xy</caption> and it’s valide xhtml 1.0 strict.
best
johannes