Re: Implement \once as music function able to operate on complex stuff. (issue 5322065)

[dak]

As an illustration: take a look at ly/property-init.ly.  It contains
dozens of commands that will cooperate with the new \once.  All of them
(well, the reverting commands don't, just because \once\revert is not
[yet?] workable in general).  That's its principal selling point.

And I don't want to hide that.  It's much more important than testing
that it will work with some custom-defined command.

http://codereview.appspot.com/5322065/