Brackets at the beginning of an AS file

I’ve seen this type of statement occasionally in AS3 files:

[Event(name="complete", type="")]

Usually they appear before the class definition and aren’t always Events, as the example above is. I’ve heard they are related to Flex somehow.

It appears to be some kind of constructor call, but I’m not sure how the bracket operators fit into the syntax (no help from Help), nor why the statement is located where it is.

Has anyone used this type of syntax, and if so, why?

Thank you!