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+# $EPIC: defer.txt,v 1.3 2006/08/01 02:17:03 sthalik Exp $
+======Synopsis:======
+__defer__ {<stuff>}
+======Description:======
+The __DEFER__ command schedules <stuff> to be executed later on when
+the client is idle, and there is no risk that if <stuff> were to destroy
+something that it would crash the client.
+Any time you want to destroy something, whether it be a DCC, a server, a open
+file, an /[[on]], a window, a log file, etc, you always run the risk that some
+alias further down the stack might have done a /wait or a /[[pause]] or a
+/[[redirect]], and is holding a reference to the thing you want to destroy.  It
+is possible that if you destroy that thing, and then the /[[wait]] or
+/[[pause]] or /[[redirect]] finishes, that the alias down further in the stack
+might try to use the object, which you destroyed, and thus it will crash the
+client.
+Now, I'm not saying that such cases are "normal" but there are sequencing
+issues that may result in it being dangerous for you to destroy something
+at certain times.  THIS IS ESPECIALLY TRUE INSIDE ONs.  If you find that
+your script can crash the client by deleting something, the first thing
+you should try is to put a /DEFER in front of the command to see if that
+fixes it.
+Obviously, if you /DEFER destroying something, it won't be destroyed
+immediately, so you can't use it in any place where it's important that
+the object is actually destroyed before you continue.
+======Example 1:======
+Here's an example that will malfunction on many versions:
+     ON #401 -1 * { on 401 - }
+     ON ^401 * { echo -- 401 hooked! $*
+     whois doesnotexist
+The reason why this crashes is because the -1 serial numbered on deletes
+both on's, but the /[[ON]] system still has a pointer to the second on and
+still intends to run it, even after it's been deleted.  Although this
+particular bug has been fixed in recent versions, it's an example of the
+kind of destruction that could cause a crash.
+So in the above example, this is the "safer" way:
+     ON #401 -1 * { defer on 401 - }
+     ON ^401 * { echo -- 401 hooked! $*
+     whois doesnotexist
+But obviously this means that the second /[[on]] will execute.  (There is no
+reasonable, portable, crash-proof way to destroy an /[[on]] so it will not run
+from a lower numbered serial number.)
+======Example 2:======
+It doesn't matter what you want to do within an /[[ON]] WINDOW_* hook, you
+probably should /DEFER it.
+======History:======
+The __DEFER__ command first appeared in EPIC4-0.9.16.