preg_match()
aaaaa: passed
ŁŁŁŁŁ: didn't pass
: passed
: passed
ŘĹ: passed

preg_match() with (*UTF8)
aaaaa: passed
ŁŁŁŁŁ: passed
: didn't pass
: didn't pass
ŘĹ: didn't pass

mb_ereg()
aaaaa: passed
ŁŁŁŁŁ: passed
: didn't pass
: didn't pass
ŘĹ: didn't pass