Intersect returns the intersection of all the paths in the input field masks.

New constructs a field mask from a list of paths and verifies that each one is valid according to the specified message type.

Union returns the union of all the paths in the input field masks.

`FieldMask` represents a set of symbolic field paths, for example: paths: "f.a" paths: "f.b.d" Here `f` represents a field in some root message, `a` and `b` fields in the message found in `f`, and `d` a field found in the message in `f.b`.