Documenting when different regexp libraries are used

The documentation hasn't been clear on which regular expression
implementations were used when e.g. interpreting different
configuration variables. In trivial cases this doesn't matter
as most regular expression metacharacters are widely supported,
but for complex expressions it can be beneficial to know.

Change-Id: I2a479aba68779cf857dac9999bc4a90ac2685838
4 files changed