NAME
       focus - Manage the input focus

SYNOPSIS
       focus
       focus window
       focus option ?arg arg ...?


DESCRIPTION
       The  focus  command is used to manage the Tk input focus.  At any given
       time, one window on each display is designated  as  the  focus  window;
       any  key  press  or key release events for the display are sent to that
       window.  It is normally up to the window manager to redirect the  focus
       among  the  top-level  windows  of a display.  For example, some window
       managers automatically set the input focus to a top-level window  when-
       ever  the  mouse  enters it;  others redirect the input focus only when
       the user clicks on a window.  Usually the window manager will  set  the
       focus  only  to  top-level windows, leaving it up to the application to
       redirect the focus among the children of the top-level.

       Tk remembers one focus window  for  each  top-level  (the  most  recent
       descendant  of  that  top-level to receive the focus);  when the window
       manager gives the focus to a top-level, Tk automatically  redirects  it
       to the remembered window.  Within a top-level Tk uses an explicit focus
       model by default.  Moving the mouse within a top-level  does  not  nor-
       mally  change  the focus;  the focus changes only when a widget decides
       explicitly to claim the focus (e.g., because of  a  button  click),  or
       when the user types a key such as Tab that moves the focus.

       The  Tcl  procedure  tk_focusFollowsMouse  may  be invoked to create an
       implicit focus model:  it reconfigures Tk so that the focus is set to a
       window  whenever  the mouse enters it.  The Tcl procedures tk_focusNext
       and tk_focusPrev implement a focus order among the windows  of  a  top-
       level;   they  are  used in the default bindings for Tab and Shift-Tab,
       among other things.

       The focus command can take any of the following forms:

       focus  Returns the path name of the focus window on  the  display  con-
              taining the application's main window,  or an empty string if no
              window in this  application  has  the  focus  on  that  display.
              Note:   it  is  better  to  specify the display explicitly using
              -displayof (see below) so that the code will  work  in  applica-
              tions using multiple displays.

       focus window
              If  the  application  currently  has the input focus on window's
              display, this command resets the input focus for  window's  dis-
              play  to window and returns an empty string.  If the application
              doesn't currently have the  input  focus  on  window's  display,
              window  will  be remembered as the focus for its top-level;  the
              next time the focus arrives at the top-level, Tk  will  redirect
              it  to  window.   If  window is an empty string then the command
              does nothing.

       focus -displayof window
              Returns the name of the focus window on the  display  containing
              window.   If the focus window for window's display isn't in this
              application, the return value is an empty string.

       focus -force window
              Sets the focus of window's display to window, even if the appli-
              cation  doesn't  currently have the input focus for the display.
              This command should be used sparingly, if  at  all.   In  normal
              usage,  an  application  should  not claim the focus for itself;
              instead, it should wait for the window manager to  give  it  the
              focus.  If window is an empty string then the command does noth-
              ing.

       focus -lastfor window
              Returns the name of the most recent window  to  have  the  input
              focus among all the windows in the same top-level as window.  If
              no window in that top-level has ever had the input focus, or  if
              the  most recent focus window has been deleted, then the name of
              the top-level is returned.  The return value is the window  that
              will  receive  the  input focus the next time the window manager
              gives the focus to the top-level.

QUIRKS
       When an internal window receives the input focus, Tk  doesn't  actually
       set  the  X  focus to that window;  as far as X is concerned, the focus
       will stay on the top-level window containing the window with the focus.
       However,  Tk  generates  FocusIn  and  FocusOut events just as if the X
       focus were on the internal window.   This approach gets around a number
       of  problems  that  would occur if the X focus were actually moved; the
       fact that the X focus is on the top-level is invisible unless you use C
       code to query the X server directly.

EXAMPLE
       To  make  a  window  that only participates in the focus traversal ring
       when a variable is set, add  the  following  bindings  to  the  widgets
       before and after it in that focus ring:
              button .before -text "Before"
              button .middle -text "Middle"
              button .after  -text "After"
              checkbutton .flag -variable traverseToMiddle -takefocus 0
              pack .flag -side left
              pack .before .middle .after
              bind .before <Tab> {
                 if {!$traverseToMiddle} {
                    focus .after
                    break
                 }
              }
              bind .after <Shift-Tab> {
                 if {!$traverseToMiddle} {
                    focus .before
                    break
                 }
              }
              focus .before


KEYWORDS
