behaviour, and they are not
thread-safe or even POSIX compatible.
</p>
<p>
Those POSIX option bits that can reasonably be mapped to PCRE2 native options
have been implemented. In addition, the option REG_EXTENDED is defined with the
value zero. This has no effect, but since programs that are written to the
POSIX interface often use it, this makes it easier to slot in PCRE2 as a
replacement library. Other POSIX options are not even defined.
</p>
<p>
There are also some options that are not defined by POSIX. 