How is the meaning of the following achieved?

Cad é mar atá tú?

Looking in the dictionary, mar áta means namely, which doesn't seem to help. Is cad é mar atá an idiom?

I found the answer here:

http://en.wiktionary.org/wiki/cad_é_mar

Literally it's - How it as that are you? (but in Munster it's - Conas tann/taoi tú?)