I opted for this particular regex as a minor safety net. If any value in %property is ever something else than L, D, or X, the regex will fail at that point. That's just a smidgen better than letting the regex skip those silently, causing the splice to pull together the wrong things.

The latter would be too clever by a half indeed; the join is very clear in my mind, and if I wanted to make it more explicit, I'd use another temporary scalar at that point instead.

Makeshifts last the longest.