It's a bit trickier, than patryk wrote:
There are parameters (you can specify several of these at the same time):
'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;
'e': eval() resulting code
And there are "modes" (if you specify several of these, the LAST one will be used):
'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;
You can find descriptions of these constants here: http://www.geocities.jp/kosako3/oniguruma/doc/API.txt