test IDs for XML (for XHTML) and HTML 4 syntax compliance

and fuck HTML 5 which allows “anything but a space”, srsly‽

oh and they are case-sensitive in XML and XHTML {1,2,5}
but case-insensitive in HTML {4,5}…

notes/cvtdat.sh

@@ -192,6 +192,10 @@ function getpc {
 function anchorIt {
 	local id=$cw idhtm idltx lbl=$line lblhtm lblltx ltxit
 
+	[[ $id = [A-Z_a-z]*([A-Z_a-z0-9.-]) ]] || die \
+	    "item identifyer ${id@Q} is not a valid ASCII xml:id NCName"
+	[[ $id = [A-Za-z]*([A-Za-z0-9_:.-]) ]] || die \
+	    "item identifyer ${id@Q} is not a valid HTML 4 id attribute"
 	idhtm=${|tohtm "$id";}
 	idltx=${|totex "$id";}
 	if [[ -z $lbl ]]; then