Docs bug: \once prefix

[DrippingTone]

The documentation for the \once prefix (both v2.14 and v2.15) at:
http://lilypond.org/doc/v2.14/Documentation/learning/tweaking-methods
says:

[...] effective only during the current musical moment before the property
reverts back to its default value.

It should say something like : "reverts back to its current value (this can be
different from the default if an \override is in effect)."

Slightly changing the example in the documentation illustrates this:

c4 d
\override NoteHead #'color = #red
e4 f |
\once \override NoteHead #'color = #green
g4 a
\revert NoteHead #'color
b c |

A single note is green, then we continue with red notes until we use \revert to
get the default color (black).


I think the learning manual can fully explain this without becoming overly
complicated (this is the natural expectation from the English keyword \once).