[Mailmunge] Context vs Filter Docs

[postfix at ptld.com]

> The Mailmunge::Context page lists all of those accessors, *plus* some
> accessors that are set only if the filter calls certain actions.

I assume you are talking about

     $ctx->bounced
     $ctx->discarded
     $ctx->in_filter_wrapup
     $ctx->message_quarantined
     $ctx->tempfailed

in the filter_message(). What do you mean they are "only set" if...? 
Does that mean the variables aren't declared sometimes? Or they always 
exist/declared but sometimes have value of undefined? Or are they always 
either true/false (1/0)?