GUEST - The tune is in ABC format - a text based system for notating tunes, especially suited for melody lines.

The standard reference is: The ABC home page (this has introduction to ABC and list of software for playing and converting ABC to print formats amongst other stuff)

but there are Mudcat threads explaining it also; see for example:

Mudcat ABC Tune Guide
What is abc format

(If you type ABC in the Filter box and set the Age drop-down to 3 years and press Refresh you'll find some other threads about ABC)

Mick