what would/should "VAR -= <text>" correspond to?

[Robert P. J. Day]

  i just ran across a situation where it would have been enormously
handy to be able to quickly remove arbitrary items from a list of
items.

  in the same way that variables support the operations

        VAR = fred barney
        VAR += wilma betty

it would have been nice to be able to do:

        VAR -= wilma bambam

the semantics being to remove (a la "filter-out") an arbitrary set of
matching strings.  if an item is not a word in the string, then
nothing happens.  no harm, no foul, with the result of the above
being that

        VAR = fred barney betty

i realize i can get the same effect by, say, writing a macro involving
"filter-out", but is there a reason the above couldn't be done?  i
just tried it and, a little to my surprise, i didn't get a syntax
error.  it didn't do anything, of course, but make didn't complain.

  does the above construct actually represent something in gnu make?
i don't see anything about it in the docs.

rday

p.s. the one problem i see is perhaps defining the meaning of
recursive expansion of such a construct, which might make all of this
moot.