User-defined functions may not be defined. However, additional functions may easily be added if access to the library source code is available. As with operators, most functions are strict with respect to undefined and error on all arguments. However, some functions are non-strict. The name of the function is case-insensitive.
V is the undefined value.
V is the error value. V is a string value. V is a list value. V is a classad value. V is a boolean value.