I have the following xquery fragment:
let $path := request:get-parameter("path",""),
$doc := util:eval($path)
where $path = "/AMM//PGBLK[1]"
I want the evaluation of this path to occur in a specific collection, namely "/db/pub".  I see the collection() function.  How do I incorporate that function in with the eval function so that the evaluation occurs in the specific scope? 
I've tried util:eval(collection('/db/pub')/$path) but get the exception "Error checking function parameter 1 in call util:eval(collection("/db/pub")/child::node()): cannot convert value of type xs:string to a node set [at line 30, column 16]"