A function call consists of the name of the function and a list of comma-separated expressions, which are the arguments to the function. Here is an example:
This function call applies the built-in function fn:concat to the values of the literal expressions "http://www.example.com/auction/" and "1001" and returns the concatenation of its arguments.
A function's signature specifies the required types of its arguments and the type of its result. The XQuery specifications (see [XQ-FO]) provide the signatures for all built-in XQuery functions. Here is the signature for the function fn:concat:
fn:concat($op1 as xs:string ?, $op2 as xs:string ?) as xs:string
This signature specifies ...