The regexp is basically saying:

^ - at the start of the line
[\w.-]+ - match one or more word characters, periods or hyphens
\@ - followed by an @
(?:[\w-]+\.)+ - then a series of either one or more word characters/hy
+phens or a period
\w+ - followed by one or more word characters
$ - then the end of line.
[download]

It looks like this is to match e-mail addresses in text .. something of the format email.address@my.email.com.

Hope that helps ..
--Foxcub