Supported options are:
i - ONIG_OPTION_IGNORECASE
x - ONIG_OPTION_EXTEND
m - ONIG_OPTION_MULTILINE
s - ONIG_OPTION_SINGLELINE
p - ONIG_OPTION_MULTILINE | ONIG_OPTION_SINGLELINE
l - ONIG_OPTION_FIND_LONGEST
n - ONIG_OPTION_FIND_NOT_EMPTY
j - ONIG_SYNTAX_JAVA
u - ONIG_SYNTAX_GNU_REGEX
g - ONIG_SYNTAX_GREP
c - ONIG_SYNTAX_EMACS
r - ONIG_SYNTAX_RUBY
z - ONIG_SYNTAX_PERL
b - ONIG_SYNTAX_POSIX_BASIC
d - ONIG_SYNTAX_POSIX_EXTENDED
e - eval() resulting code
Constants above are from Oniguruma regexp library, which is used internally. Default value for PHP 5.2.x is 'pr'.
