NAME

       focus - Manage the input focus

SYNOPSIS

       focus
       focus window
       focus option ?arg arg ...?
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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
       whenever  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 normally 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 containing 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 applications 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 display to window and returns an empty string.  If the application does
              not 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 is not 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 application does not 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 nothing.

       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 does not 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

       events, focus, keyboard, top-level, window manager