RE: font-lock-maximum-decoration should be 2 by default?

[Drew Adams]

> > Interesting. I am curious of reasons for that.
> 
> Performance.  You don't gain much by omitting some fontifications
> nowadays.  The variable was introduced to get snappier redisplay;
> since the need for that is no longer valid, the default was set to t.

Do you have any proof of that being _the_ reason it was introduced: just for
performance?

FWIW, that would suggest that the default was initially something other than
`t', which contradicts what Stefan has conjectured.  (I too would guess that the
original default value might not have been `t', but I do not recall.)

And when you say "is no longer valid", apparently you mean that at least since
Emacs 20 it has not been valid, since as you have said elsewhere, 20.1 is when
it became `t'.

I would be surprised if the ability for users to pick the highlighting level
they wanted - with whatever motivation - was not a reason for introducing this
variable.  IOW, my guess is that it has always been about letting users get the
amount of highlighting they want - for whatever reasons, not necessarily for
better redisplay performance.

That some user on a slow machine, long ago, might have chosen minimal
highlighting in part because of performance in no way supports a view that that
is the only reason for a user to choose less highlighting, and it in no way
supports the view that the variable was added only because of slow redisplay.

The variable, now as in the past, gives users control over the amount of
highlighting font lock provides.  Nothing more or less than that.

Yes, that user control is hidden to some extent by the default value being `t',
and to some extent it is stymied by the scarcity of libraries that provide
multiple levels.  Still, the variable lets users choose.