eregi() pattern

Hello: eregi() is a function to find a match string with a pattern. This pattern is similar to Perl's one (or is the same). Well I readed some documents to create this pattern but I'm still confusing to use some non-usascii chars. (acutes, radios, graves, umlauts, etc., for example). Well here is my question: Does somebody knows a nice document that explains this use of non-usascii chars on a pattern? In wich Language Codification this pattern compares the string? Thanks a lot for your help. Mario Soto mario_s@amigo.net.gt -.-.-.-