Maybe for you, but the capabilities and mechanics of the filters is not where I run into trouble, and regexes would not make much difference. Gmail filters are

Maybe for you, but the capabilities and mechanics of the filters is not where I run into trouble, and regexes would not make much difference. Gmail filters are already pretty darn good for my needs. Figuring out the correct conditions conceptually is the hard part. OTOH, I'm told you can't apply Sieve filters retroactively? That sounds completely awful.