C++: Missing documentation for MODOP_EXPR

[Gabriel Dos Reis]

Mark,

  While working on the new C++ pretty-printer, I came to realize that 
MODOP_EXPR is documented nowhere.  The only comment I can find is this:

/* A whole bunch of tree codes for the initial, superficial parsing of
   templates.  */

from cp/cp-tree.def.  While the meaning of most of those "bunch of
tree codes" may be infered from their names and some familiarity with
the C++ front end, that of MODOP_EXPR remains obscure to me.

Could you enlighten me?

-- Gaby