in reply to Re^2: regex is not working as I intended
in thread regex is not working as I intended

I forgot to mention that this regex is used repeatedly on the same string to parse out parameter and value pairs, such as the following:

radius = 3, density = .014, URL = "", max_no_of_attempts = 4

That is why the lookbehind and lookahead assertions are used, even though they cannot possibly match at the beginning or end of the overall parameter string, they can match at intermediate positions as the regex is used to walk over the value of the parameter string parsing out individual parm and value pairs.