NAME
       grab  -  Confine  pointer  and keyboard events to a window
       sub-tree

SYNOPSIS
       grab ?-global? window

       grab option ?arg arg ...?


DESCRIPTION
       This command implements simple pointer and keyboard  grabs
       for Tk.  Tk's grabs are different than the grabs described
       in the Xlib documentation.  When a grab is set for a  par-
       ticular  window,  Tk  restricts  all pointer events to the
       grab window and its descendants in Tk's window  hierarchy.
       Whenever  the pointer is within the grab window's subtree,
       the pointer will behave exactly the same as if  there  had
       been no grab at all and all events will be reported in the
       normal fashion.  When  the  pointer  is  outside  window's
       tree,  button presses and releases and mouse motion events
       are reported to window, and window entry and  window  exit
       events   are  ignored.   The  grab  subtree  ``owns''  the
       pointer: windows outside the grab subtree will be  visible
       on  the screen but they will be insensitive until the grab
       is released.  The tree of windows underneath the grab win-
       dow  can  include  top-level windows, in which case all of
       those top-level windows and their  descendants  will  con-
       tinue to receive mouse events during the grab.

       Two  forms  of  grabs  are possible:  local and global.  A
       local grab affects only the grabbing application:   events
       will  be reported to other applications as if the grab had
       never occurred.  Grabs are local  by  default.   A  global
       grab  locks  out  all  applications on the screen, so that
       only the given subtree of the grabbing application will be
       sensitive  to  pointer events (mouse button presses, mouse
       button releases, pointer motions, window entries, and win-
       dow  exits).   During global grabs the window manager will
       not receive pointer events either.

       During local grabs, keyboard events (key presses  and  key
       releases) are delivered as usual:  the window manager con-
       trols which application receives keyboard events,  and  if
       they  are  sent  to any window in the grabbing application
       then they are redirected to the focus  window.   During  a
       global  grab  Tk  grabs  the keyboard so that all keyboard
       events are always sent to the grabbing  application.   The
       focus  command  is still used to determine which window in
       the application receives the keyboard  events.   The  key-
       board grab is released when the grab is released.

       Grabs apply to particular displays.  If an application has
       windows on multiple  displays  then  it  can  establish  a
       separate  grab  on each display.  The grab on a particular
       display affects only the windows on that display.   It  is
       possible for different applications on a single display to
       have simultaneous local grabs, but  only  one  application
       can have a global grab on a given display at once.

       The grab command can take any of the following forms:

       grab ?-global? window
              Same as grab set, described below.

       grab current ?window?
              If  window  is  specified,  returns the name of the
              current grab window in this  application  for  win-
              dow's  display,  or  an empty string if there is no
              such window.  If window  is  omitted,  the  command
              returns  a  list whose elements are all of the win-
              dows grabbed by this application for all  displays,
              or an empty string if the application has no grabs.

       grab release window
              Releases the grab on window if there is one, other-
              wise does nothing.  Returns an empty string.

       grab set ?-global? window
              Sets  a  grab  on  window.  If -global is specified
              then the grab is global, otherwise it is local.  If
              a  grab  was already in effect for this application
              on  window's  display  then  it  is   automatically
              released.  If there is already a grab on window and
              it has the same global/local form as the  requested
              grab,  then  the  command does nothing.  Returns an
              empty string.

       grab status window
              Returns none if no grab is currently set on window,
              local  if a local grab is set on window, and global
              if a global grab is set.


BUGS
       It took an incredibly complex and gross implementation  to
       produce the simple grab effect described above.  Given the
       current implementation, it isn't safe for applications  to
       use  the Xlib grab facilities at all except through the Tk
       grab procedures.  If applications try  to  manipulate  X's
       grab mechanisms directly, things will probably break.

       If  a  single  process  is  managing  several different Tk
       applications, only one of those applications  can  have  a
       local  grab for a given display at any given time.  If the
       applications are in different processes, this  restriction
       doesn't exist.
KEYWORDS
       grab, keyboard events, pointer events, window
