Conditionally color all tweaked objects

[Urs Liska]

Hi,

is it possible somehow to hook into the engraving process and color all
grobs that have been manually tweaked?

In my library I have a 'draft mode'. All my functions or shorthands that
tweak the positioning have a counterpart in draft mode. The draft mode
functions basically call the normal functions and add coloring to them.
This way I can compile a score in draft mode and immediately see where I
had to apply some manual interventions.

While this is quite useful in the process of finishing a score (and also
to evaluate LilyPond's performance) it obviously only works with tweaks
applied through my custom functions. But it would only be _really_
useful if I could highlight _all_ manual interventions.
Of course it isn't a viable solution to write such functions for any
tweak I'm applying so I thought if it would be possible to do such a
thing in a more fundamental way.

So would such a thing be possible, maybe in Scheme?
Or if that's not possible in Scheme would that be an interesting feature
request?

Urs