NAME

       Tk::focus - Manage the input focus

SYNOPSIS

          $widget->focus

          $widget->focusOption

          $widget->focusNext

          $widget->focusPrev

          $widget->focusFollowsMouse

DESCRIPTION

       The focus methods are 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 method 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
       methods focusNext and 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 methods can take any of the following forms:

       $widget->focusCurrent
           Returns the focus window on the display containing the $widget,  or an empty string if
           no window in this application has the focus on that display.

       $widget->focus
           If the application currently has the input focus on $widget's display, this command
           resets the input focus for $widget's display to $widget and returns an empty string.
           If the application doesn't currently have the  input focus on $widget's display,
           $widget 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 $widget.

       $widget->focusForce
           Sets the focus of $widget's display to $widget, even if the application 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.

       $widget->focusLastfor
           Returns the name of the most recent window to have the input focus among all the
           windows in the same top-level as $widget.  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 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.

       $widget->focusNext
       $widget->focusPrev
           focusNext is a utility method used for keyboard traversal, but can be useful in other
           contexts.  It sets the focus to the ``next'' window after $widget in focus order.  The
           focus order is determined by the stacking order of windows and the structure of the
           window hierarchy.  Among siblings, the focus order is the same as the stacking order,
           with the lowest window being first.  If a window has children, the window is visited
           first, followed by its children (recursively), followed by its next sibling.  Top-
           level windows other than $widget are skipped, so that focusNext never returns a window
           in a different top-level from $widget.

           After computing the next window, focusNext examines the window's -takefocus option to
           see whether it should be skipped.  If so, focusNext continues on to the next window in
           the focus order, until it eventually finds a window that will accept the focus or
           returns back to $widget.

           focusPrev is similar to focusNext except that it sets the focus to the window just
           before $widget in the focus order.

       $widget->focusFollowsMouse
           focusFollowsMouse changes the focus model for the application to an implicit one where
           the window under the mouse gets the focus.  After this procedure is called, whenever
           the mouse enters a window Tk will automatically give it the input focus.  The focus
           command may be used to move the focus to a window other than the one under the mouse,
           but as soon as the mouse moves into a new window the focus will jump to that window.
           Note: at present there is no built-in support for returning the application to an
           explicit focus model;  to do this you'll have to write a script that deletes the
           bindings created by focusFollowsMouse.

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.

CAVEATS

       Note that for the Canvas widget, the call to focus has to be fully qualified. This is
       because there is already a focus method for the Canvas widget, which sets the focus on
       individual canvas tags.

           $canvas->Tk::focus

KEYWORDS

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