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     NAME
          update - Process pending events and/or when-idle handlers

     SYNOPSIS
          update ?idletasks?
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     DESCRIPTION
          This command is used to bring the entire application world
          ``up to date.''  It flushes all pending output to the
          display,  waits for the server to process that output and
          return errors or events, handles all pending events of any
          sort (including when-idle handlers), and repeats this set of
          operations until there are no pending events, no pending
          when-idle handlers, no pending output to the server, and no
          operations still outstanding at the server.

          If the idletasks keyword is specified as an argument to the
          command, then no new events or errors are processed;  only
          when-idle idlers are invoked.  This causes operations that
          are normally deferred, such as display updates and window
          layout calculations, to be performed immediately.

          The update idletasks command is useful in scripts where
          changes have been made to the application's state and you
          want those changes to appear on the display immediately,
          rather than waiting for the script to complete.  Most
          display updates are performed as idle handlers, so update
          idletasks will cause them to run.  However, there are some
          kinds of updates that only happen in response to events,
          such as those triggered by window size changes; these
          updates will not occur in update idletasks.

          The update command with no options is useful in scripts
          where you are performing a long-running computation but you
          still want the application to respond to user interactions;
          if you occasionally call update then user input will be
          processed during the next call to update.


     KEYWORDS
          event, flush, handler, idle, update