It's nicer when both bits of the abbreviation are the same length?

I hadn't thought of that, though the thought has just occurred to me that 'exp' by itself, shorn of the 'reg' prefix, makes a more comprehensible abbreviation of 'expression' than 'ex' does.

I was thinking that. I think I use regexp occasionally but regex more. I *think* I learned regexp first, but it eroded quickly, but I'm not sure, it could have been the other way round.