Function: ad-add-advice

Add a piece of ADVICE to FUNCTION's list of advices in CLASS.

NAME is the advice name; PROTECTED is a flag specifying whether
to protect against non-local exits; ENABLED is a flag specifying
whether to initially enable the advice; and DEFINITION has the
form (advice . LAMBDA), where LAMBDA is a lambda expression.

If FUNCTION already has a piece of advice with the same name,
then POSITION is ignored, and the old advice is overwritten with
the new one.

If FUNCTION already has one or more pieces of advice of the
specified CLASS, then POSITION determines where the new piece
goes. POSITION can either be `first', `last' or a number (where
0 corresponds to `first', and numbers outside the valid range are
mapped to the closest extremal position).

If FUNCTION was not advised already, its advice info will be
initialized. Redefining a piece of advice whose name is part of
the cache-id will clear the cache.

See Info node `(elisp)Computed Advice' for detailed documentation. (fn FUNCTION ADVICE CLASS POSITION)