(doc help) set vs. override

[Graham Percival]

Here's what I came up with.  It's probably inaccurate and misleading, 
because I don't understand what I'm talking about.  If you can correct 
this, please do.  Please do *not* attempt to explain it.  Just change 
the text below so that I can add it to the manual.
- Graham

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@node \set, \override, and \tweak
@section \set, \override, and \tweak

There are three different commands which modify properties.

@itemize @bullet

@item @code{\set} changes properties of a context, and can modify
more than one graphical object.  For example, @code{fontSize} is
a context property (and therefore modified with @code{\set})
because it changes the behavior of several types of grobs
(noteheads, rests, etc).

@item @code{\override} changes properties which are specific to
one graphical object.  For example,

@item @code{\tweak} changes properties of an object which results
directly from input.  For example, @code{\tweak #'color #red} will
change the color of the next object.

@end itemize

As a rule of thumb, if you can figure out a single type of Grob that
the tweak would modify, then it probably requires an @code{\override}.