Indexing array columns.

I've been searching the manual looking for information about the effects of indexing an array column but haven't found any information as of yet. 

Does anyone have any information on how the indexes work for arrayed columns? 

Does/Can the index track each element in the array, or does it track only the array as a whole? 

How can I increase the speed of a query like: SELECT * FROM table WHERE 123 = ANY(array_of_ints); ?

Thanks,

Josh