[TxMt] Syntax Highlighting regex question

I am making a syntax module for the Rebol language and I am having trouble getting some keywords to match properly. This expression works:

match = "(action!|any-block!|any-function!|)"

but it is not ideal for I needed it to work with word boundaries. When I include word boundaries in the regex, the rule is never matched.

match = "\<(action!|any-block!|any-function!|)\>"

I think this is a problem with the exclamation point "!". I have tried using it with these escape sequences: !, \!, \041 \041; with no luck so far.

I had the same problem with keywords having the question mark "?" in them, ie:

match = "\<(about|abs|absolute|action?|add|alert|type?)\>"

Ideas would be most welcome. Is there a limitation in the regex engine?

Thanks, Jaime