Regular Expression Hell?

[Akira Kiyomiya]

Okay, these two regular expression codes are from Python Essential Reference
book and I am pretty confused about these.

Could someone dare to explan step by step?

e_mail = re.compile(r'([a-zA-Z][\w-]*@[\w-]+(?:\.[w-]+)*)')

# I know [a-zA-Z] any lower or upper word.....[\w-]??  any alphabetical
character??  what is "-" after "\w"?
# I know @, you need it for the e-mail....   Then, I am lost....

URL = re.compile(r'((ftp | http)://[\w-]+(?:\.[\w-]+)*(?:/[\w-]*)*)')

# I know ftp or http part plus "://" you need it for URL.  Then,..... I am
lost....


Akira