ParamIsDefault
ParamIsDefault (pName)
The ParamIsDefault function determines if an optional user function parameter pName was specified during the function call. It returns 1 when pName is default (not specified) or it returns 0 when it was specified.
Details
ParamIsDefault works only in the body of a user function and only with optional parameters. The variable name must be valid at compile time; you cannot defer lookup to runtime with $.