What does the code mean?

[Á÷À˵ÄË«Óã]

DATE(y,m,1)-(WEEKDAY(DATE(y,m,1))-1)+{0;1;2;3;4;5}*7+{1,2,3,4,5,6,7}-1
I acquired the code from NG.
But I can't understand it.
Can anyone explain it for me?
Thanks in advance.
--

 

[Trevor Shuttleworth]

Not sure how it works but it looks to calculate the last Sunday prior to the
month entered.

For example:

=DATE(2005,9,1)-(WEEKDAY(DATE(2005,9,1))-1)+{0;1;2;3;4;5}*7+{1,2,3,4,5,6,7}-1
gives 28/08/2005 which is a Sunday

Regards

Trevor