This function returns true if expr is of type range, and false otherwise.

An expression of type range (also called type `..`) has two operands, the expression on the left-hand side and the expression on the right-hand side. These two operands are separated by an ellipsis (..) .

The optional parameter typespec may be used to specify a type that the operands of expr must also satisfy. The typespec parameter may be used with either form (range or `..`) of the type.