Here's the code I am currently using. This is intended to HTML-highlight the left-side (search) text of a Perl regex:

        my $HighlightText = $CgiArgsRef->{'RawValue'};
        $HighlightText =~ s/&/&/go;
        $HighlightText =~ s/  /  /go;              # also use nor
+mal spaces so line wrap is still possible
        $HighlightText =~ s/\t/     /go; # also use nor
+mal spaces so line wrap is still possible
        $HighlightText =~ s/</&lt;/go;
        $HighlightText =~ s/>/&gt;/go;
        $HighlightText =~ s/\r\n/<br>/go;
                        
        # escaped characters
        $HighlightText =~ s/(\\\S)/<span class="escapedregexhighlight"
+>$1<\/span>/gso;

        my $n = 1;
        # groupings like (..)
        $HighlightText =~ s/([^\\]?|^)(\()(.+?[^\\])(\))/sprintf("%s<s
+pan class=\"searchregexhighlight\">%s<\/span><span class=\"groupregex
+textcolor\">%s<\/span><span class=\"searchregexhighlight\">%s<\/span>
+<span class=\"parametersup\">\0x00%s<\/b><\/span>",$1,$2,$3,$4,$n++)/
+gsoe;

        # single chars like . * ^ $ ? + and aggregates like {} and []
        $HighlightText =~ s/([^\\]|^)([\.\+\*\?]+|[\^\$\(]|\)\+?\??\*?
+\{?\d*,?\d*\}?|\[.+?\]\+?\??\*?\{?\d*,?\d*\}?|\{\d*,?\d*\})/$1<span c
+lass="searchregexhighlight">$2<\/span>/gso;


        # other characters
        $HighlightText =~ s/\\{0}(\\[\w\s\d])/<span class="searchregex
+highlight">$1<\/span>$3/gso;

        # put back the '$' in parameter subscripts
        $HighlightText =~ s/\0x00/\$/go;

        $HighlightText =~ s/[\r\n]+/<br>\n/go;
[download]

As mentioned, the main problem is that while this handles basic (a|b|c) groupings, it doesn't do nested groupings like (aaaa(b|c)) or ((?=pretext)aaaa). And because it's using regex to parse regex, there are other things that it doesn't do right when there are many special metacharacters in a row like a{1,3}.*?[def]+.

So, while I was really looking for something better like a do-all Perl module, I'd be happy for any suggestions that you might have to improve my existing code.

thanks!