The _c_l_i_e_n_t_D_a_t_a parameter to _p_r_o_c is a copy of the _c_l_i_e_n_t_D_a_t_a argument
given to TTTTkkkk____DDDDooooWWWWhhhheeeennnnIIIIddddlllleeee. Typically, _c_l_i_e_n_t_D_a_t_a points to a data structure
containing application-specific information about what _p_r_o_c should do.
TTTTkkkk____CCCCaaaannnncccceeeellllIIIIddddlllleeeeCCCCaaaallllllll may be used to cancel one or more previous calls to
TTTTkkkk____DDDDooooWWWWhhhheeeennnnIIIIddddlllleeee: if there is a TTTTkkkk____DDDDooooWWWWhhhheeeennnnIIIIddddlllleeee handler registered for _p_r_o_c
and _c_l_i_e_n_t_D_a_t_a, then it is removed without invoking it. If there is more
than one handler on the idle list that refers to _p_r_o_c and _c_l_i_e_n_t_D_a_t_a, all
of the handlers are removed. If no existing handlers match _p_r_o_c and
_c_l_i_e_n_t_D_a_t_a then nothing happens.
TTTTkkkk____DDDDooooWWWWhhhheeeennnnIIIIddddlllleeee is most useful in situations where (a) a piece of work will
have to be done but (b) it's possible that something will happen in the
near future that will change what has to be done, or require something
different to be done. TTTTkkkk____DDDDooooWWWWhhhheeeennnnIIIIddddlllleeee allows the actual work to be
deferred until all pending events have been processed. At this point the
exact work to be done will presumably be known and it can be done exactly
once.
For example, TTTTkkkk____DDDDooooWWWWhhhheeeennnnIIIIddddlllleeee might be used by an editor to defer display
updates until all pending commands have been processed. Without this
feature, redundant redisplays might occur in some situations, such as the