What is the <@ operator in PostgreSQL 8.4?

I am having trouble decyphering what this operator is doing. I know that it is somehow comparing the array's, but I can find no documentation on it. I also have tried >@ but that seems to error. Google yealded bad results ad when I search for "at operator" it isn't very specific. Any information would be much apprecia开发者_如何学JAVAted.

I also have not (at least I don't think so) defined any new operators in the database.

SELECT id 
FROM organizations
WHERE  ARRAY[56] <@ ancestry

From the manual:

<@  is contained by

When your array ancestry has the value 56, the result will be true.