g PCRE2 matching
function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
setting this option can give more POSIX-like behaviour in some situations.
<pre>
  REG_NOTEOL
</pre>
The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching
function.
<pre>
  REG_STARTEND
</pre>
When this option is set, the subject string starts at <i>string</i> +
<i>pmatch[0].rm_so</i> and ends at <i>string</i> + <i>pmatch[0].rm_eo</i>, which
should point to the first character beyond the string.