Re: [Groff] proposal: add variable traps to groff.

[Tadziu Hoffmann]

> A variable trap that triggers whenever a variable (register and
> string, maybe even diversion, environment, macro) is accessed, i.e.
> created, deleted, changed, read.  The trap macro gets a description
> of the variable (register or string) and of the access (action with
> data).  The trap macro can modify the result of the action and can
> have additional side effects.

Essentially, we already have a mechanism to trap a "normal"
write to a register -- simply redefine "nr" (but you have to
do all the administrative work of how to deal with which
register yourself).  Now all we need is a way to redefine
escape sequences \n, \R, etc. ... :-)