/[=foo=]/
Warning: preg_match(): Compilation failed: POSIX collating elements are not supported at offset 0 in /in/5oVpP on line 11
/[:foo:]/
Warning: preg_match(): Compilation failed: POSIX named classes are supported only within a class at offset 0 in /in/5oVpP on line 11
/[.foo.]/
Warning: preg_match(): Compilation failed: POSIX collating elements are not supported at offset 0 in /in/5oVpP on line 11