https://chat.stackexchange.com/transcript/message/50343148#50343148

notes/cvtdat.sh

@@ -192,10 +192,14 @@ function getpc {
 function anchorIt {
 	local id=$cw idhtm idltx lbl=$line lblhtm lblltx ltxit
 
+	[[ $id = +([\ -~]) ]] || die \
+	    "item identifyer ${id@Q} must be comprised of printable ASCII"
 	[[ $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"
+	[[ $id = *[\"\#\'\(\),=\{\}%\ \~\\]* ]] && die \
+	    "item identifyer ${id@Q} contains characters prohibited in Tₑχ"
 	local -l idlc=$id
 	local idid=ID_${idlc//-/D}
 	idid=${idid//./P}