Mimicking Conditionals   There are two common types of regex
conditionals in those libraries: lookaround-based and capturing-
group-based. I'll get to the former type in a bit, but first,
I'll address capturing-group-based conditionals, which are able
to base logic on whether an optional capturing group has
participated in the match so far. Here's an example:       Note
that to use it without an "else" part, you still need to include
the second empty backreference (in this case, "\3") at the end,
like this:   As a brief explanation of how that works, there's
an empty alternation option within the lookahead at the
beginning which is used to cancel the effect of the lookahead,
while at the same time, the intentionally empty capturing groups
within the alternation are exploited to base the then/else part
on which option in the lookahead matched. However, there are a
couple issues:    • This doesn't work with some regex engines,
due to how they handle backreferences for non-participating
capturing groups. For exam