 a
set of single-character alternatives such as (a|e|i|o|u). In general, the
simplest construction that provides the required behaviour is usually the most
efficient. Jeffrey Friedl's book contains a lot of useful general discussion
about optimizing regular expressions for efficient performance. This document
contains a few observations about PCRE2.
</P>
<P>
Using Unicode character properties (the \p, \P, and \X escapes) is slow,
because PCRE2 has to use a multi-stage table lookup whenever it needs a
charac