The parser in extendvars.php is a bit buggy. It can't handle cases where there
are parentheses inside strings its handling. For example:
(:set subtotalwords='(=if regmatch "/<0*(?:7)>$/" "<04>") 0
"{$subtotalwords}"':)
doesn't work, because the first ')' is taken as the end of the if condition,
even though its inside a quoted regular expression.