This procedure is defined in the server but not documented via ad_proc or proc_doc and may be intended as a private interface.
The procedure is defined as:
proc ::xowiki::validate_form_form {} {
upvar form form
if {$form eq ""} {return 1}
dom parse -simple -- [lindex $form 0] doc
$doc documentElement root
return [expr {$root ne "" && [$root nodeName] eq "form"}]
}