There's a popular tune used for _kidush_ on the nights of the _shalosh r'galim_. ([It's available on YouTube](http://www.youtube.com/watch?v=QViMUMWOqVs "Kiddush for Pesach - Karaoke Style") (but ignore the "_shehechiyanu_" part of that recording).)

1. What's its origin?
2. Does it have the _minhag_-status or immutability [ascribed](http://judaism.stackexchange.com/a/10018) to [some](http://judaism.stackexchange.com/a/2389) of the tunes that we use for prayers?