Question

What is the complete list of characters matched by the escape sequence \s in PHP ?
Some regex flavors include vertical space and other characters in this escape sequence.

Answer 1

From pcrepattern specifications page:

Generic character types

\s     any white space character

For compatibility with Perl, \s did not used to match the VT character
(code 11), which made it different from the the POSIX “space” class.
However, Perl added VT at release 5.18, and PCRE followed suit at
release 8.34. The default \s characters are now HT (9), LF (10), VT
(11), FF (12), CR (13), and space (32), which are defined as white
space in the “C” locale. This list may vary if locale-specific
matching is taking place. For example, in some locales the
“non-breaking space” character (\xA0) is recognized as white space,
and in others the VT character is not.

So \s will match 5 characters plus more depending on:

1. PCRE library version
2. Locale setting

This test compares the result of preg_match across various versions of PHP.