Con 2230 infobox seemore

I would rather simplifying this regex to
* `/rgba\(\d+, \d+, \d+, (0|0\.\d+)\)/` or
* `/rgba\((\d{1,3}, ){3}(0|0\.\d+)\)/` (this adds one more capturing group before the 'alpha')  or
* `/rgba\([\d, ]{7,13}, (0|0\.\d+)\)/` or even
* `/rgba\([\d, ]+(0|0\.\d+)\)/`.

Let me explain why.
* I've checked all four major browsers and the output of the `getPropertyValue()` is consistent.
* The alpha we are looking for can be `0` or a floating point number lower than `0`. When the opacity value would be `1`, the browser returns just `rgb(#r, #g, #b)`, so the matching fails already on 4th char.
* I think we can drop the global switch `/(...)/g`--even if browser somehow returned two matches for the regex, `exec()` is run only once, i.e. we pick just the first match.

I'm not a regex ace, maybe someone else could say if my thinking is right.