I have this simple Hello world code from here, and can't find what does line xsd mean, and how to use it. Where is this file located and is it necessary?
module scribble.example.Basic;
type <xsd> "{http://scribble.org/examples}Greetings" from "HelloWorld.xsd" as Greetings;
global protocol HelloWorld (role Me, role World) {
hello(Greetings) from Me to World;
hello(Greetings) from World to Me;
}