menu, tk_menuSetFocus - Create and manipulate 'menu' widgets and
menubars
menu pathName ?options?
tk_menuSetFocus pathName
-activebackground -borderwidth -foreground
-activeborderwidth -cursor -relief
-activeforeground -disabledforeground -takefocus
-background -font
See the options manual entry for details on the standard
options.
Command-Line Name: -postcommand
Database Name: postCommand
Database Class: Command
- If this option is specified then it provides a Tcl command to execute each
time the menu is posted. The command is invoked by the post widget
command before posting the menu. Note that in Tk 8.0 on Macintosh and
Windows, all post-commands in a system of menus are executed before any of
those menus are posted. This is due to the limitations in the individual
platforms' menu managers.
Command-Line Name: -selectcolor
Database Name: selectColor
Database Class: Background
- For menu entries that are check buttons or radio buttons, this option
specifies the color to display in the indicator when the check button or
radio button is selected.
Command-Line Name: -tearoff
Database Name: tearOff
Database Class: TearOff
- This option must have a proper boolean value, which specifies whether or
not the menu should include a tear-off entry at the top. If so, it will
exist as entry 0 of the menu and the other entries will number starting at
1. The default menu bindings arrange for the menu to be torn off when the
tear-off entry is invoked. This option is ignored under Aqua/Mac OS X,
where menus cannot be torn off.
Command-Line Name: -tearoffcommand
Database Name: tearOffCommand
Database Class: TearOffCommand
- If this option has a non-empty value, then it specifies a Tcl command to
invoke whenever the menu is torn off. The actual command will consist of
the value of this option, followed by a space, followed by the name of the
menu window, followed by a space, followed by the name of the name of the
torn off menu window. For example, if the option's value is “a
b” and menu .x.y is torn off to create a new menu
.x.tearoff1, then the command “a b .x.y
.x.tearoff1” will be invoked. This option is ignored under
Aqua/Mac OS X, where menus cannot be torn off.
Command-Line Name: -title
Database Name: title
Database Class: Title
- The string will be used to title the window created when this menu is torn
off. If the title is NULL, then the window will have the title of the
menubutton or the text of the cascade item from which this menu was
invoked.
Command-Line Name: -type
Database Name: type
Database Class: Type
- This option can be one of menubar, tearoff, or
normal, and is set when the menu is created. While the string
returned by the configuration database will change if this option is
changed, this does not affect the menu widget's behavior. This is used by
the cloning mechanism and is not normally set outside of the Tk library.
The menu command creates a new top-level window (given by
the pathName argument) and makes it into a menu widget. That menu
widget can either be used as a pop-up window or applied to a toplevel
(with its -menu option) to make it into the menubar for that
toplevel. Additional options, described above, may be specified on the
command line or in the option database to configure aspects of the menu such
as its colors and font. The menu command returns its pathName
argument. At the time this command is invoked, there must not exist a window
named pathName, but pathName's parent must exist.
A menu is a widget that displays a collection of one-line entries
arranged in one or more columns. There exist several different types of
entries, each with different properties. Entries of different types may be
combined in a single menu. Menu entries are not the same as entry widgets.
In fact, menu entries are not even distinct widgets; the entire menu is one
widget.
Menu entries are displayed with up to three separate fields. The
main field is a label in the form of a text string, a bitmap, or an image,
controlled by the -label, -bitmap, and -image options
for the entry. If the -accelerator option is specified for an entry
then a second textual field is displayed to the right of the label. The
accelerator typically describes a keystroke sequence that may be used in the
application to cause the same result as invoking the menu entry. This is a
display option, it does not actually set the corresponding binding (which
can be achieved using the bind command). The third field is an
indicator. The indicator is present only for checkbutton or
radiobutton entries. It indicates whether the entry is selected or not, and
is displayed to the left of the entry's string.
In normal use, an entry becomes active (displays itself
differently) whenever the mouse pointer is over the entry. If a mouse button
is released over the entry then the entry is invoked. The effect of
invocation is different for each type of entry; these effects are described
below in the sections on individual entries.
Entries may be disabled, which causes their labels and
accelerators to be displayed with dimmer colors. The default menu bindings
will not allow a disabled entry to be activated or invoked. Disabled entries
may be re-enabled, at which point it becomes possible to activate and invoke
them again.
Whenever a menu's active entry is changed, a
<<MenuSelect>> virtual event is send to the menu. The active
item can then be queried from the menu, and an action can be taken, such as
setting context-sensitive help text for the entry.
The most common kind of menu entry is a command entry, which
behaves much like a button widget. When a command entry is invoked, a Tcl
command is executed. The Tcl command is specified with the -command
option.
A separator is an entry that is displayed as a horizontal dividing
line. A separator may not be activated or invoked, and it has no behavior
other than its display appearance.
A checkbutton menu entry behaves much like a checkbutton widget.
When it is invoked it toggles back and forth between the selected and
deselected states. When the entry is selected, a particular value is stored
in a particular global variable (as determined by the -onvalue and
-variable options for the entry); when the entry is deselected
another value (determined by the -offvalue option) is stored in the
global variable. An indicator box is displayed to the left of the label in a
checkbutton entry. If the entry is selected then the indicator's center is
displayed in the color given by the -selectcolor option for the
entry; otherwise the indicator's center is displayed in the background color
for the menu. If a -command option is specified for a checkbutton
entry, then its value is evaluated as a Tcl command each time the entry is
invoked; this happens after toggling the entry's selected state.
A radiobutton menu entry behaves much like a radiobutton widget.
Radiobutton entries are organized in groups of which only one entry may be
selected at a time. Whenever a particular entry becomes selected it stores a
particular value into a particular global variable (as determined by the
-value and -variable options for the entry). This action
causes any previously-selected entry in the same group to deselect itself.
Once an entry has become selected, any change to the entry's associated
variable will cause the entry to deselect itself. Grouping of radiobutton
entries is determined by their associated variables: if two entries have the
same associated variable then they are in the same group. An indicator
diamond is displayed to the left of the label in each radiobutton entry. If
the entry is selected then the indicator's center is displayed in the color
given by the -selectcolor option for the entry; otherwise the
indicator's center is displayed in the background color for the menu. If a
-command option is specified for a radiobutton entry, then its value
is evaluated as a Tcl command each time the entry is invoked; this happens
after selecting the entry.
A cascade entry is one with an associated menu (determined by the
-menu option). Cascade entries allow the construction of cascading
menus. The postcascade widget command can be used to post and unpost
the associated menu just next to of the cascade entry. The associated menu
must be a child of the menu containing the cascade entry (this is needed in
order for menu traversal to work correctly).
A cascade entry posts its associated menu by invoking a Tcl
command of the form
where menu is the path name of the associated menu, and x and
y are the root-window coordinates of the upper-right corner of the
cascade entry. On Unix, the lower-level menu is unposted by executing a Tcl
command with the form
where menu is the name of the associated menu. On other platforms, the
platform's native code takes care of unposting the menu.
If a -command option is specified for a cascade entry then
it is evaluated as a Tcl command whenever the entry is invoked. This is not
supported on Windows.
A tear-off entry appears at the top of the menu if enabled with
the -tearoff option. It is not like other menu entries in that it
cannot be created with the add widget command and cannot be deleted
with the delete widget command. When a tear-off entry is created it
appears as a dashed line at the top of the menu. Under the default bindings,
invoking the tear-off entry causes a torn-off copy to be made of the menu
and all of its submenus.
Any menu can be set as a menubar for a toplevel window (see
toplevel command for syntax). On the Macintosh, whenever the toplevel
is in front, this menu's cascade items will appear in the menubar across the
top of the main monitor. On Windows and Unix, this menu's items will be
displayed in a menubar across the top of the window. These menus will behave
according to the interface guidelines of their platforms. For every menu set
as a menubar, a clone menu is made. See the CLONES section for more
information.
As noted, menubars may behave differently on different platforms.
One example of this concerns the handling of checkbuttons and radiobuttons
within the menu. While it is permitted to put these menu elements on
menubars, they may not be drawn with indicators on some platforms, due to
system restrictions.
Certain menus in a menubar will be treated specially. On the
Macintosh, access to the special Application, Window and Help menus is
provided. On Windows, access to the Windows System menu in each window is
provided. On X Windows, a special right-justified help menu may be provided
if Motif menu compatibility is enabled. In all cases, these menus must be
created with the command name of the menubar menu concatenated with the
special name. So for a menubar named .menubar, on the Macintosh, the special
menus would be .menubar.apple, .menubar.window and .menubar.help; on
Windows, the special menu would be .menubar.system; on X Windows, the help
menu would be .menubar.help.
When Tk sees a .menubar.apple menu as the first menu in a menubar
on the Macintosh, that menu's contents make up the first items of the
Application menu whenever the window containing the menubar is in front.
After all of the Tk-defined items, the menu will have a separator, followed
by all standard Application menu items. Such a .apple menu must be present
in a menu when that menu is first configured as a toplevel's menubar,
otherwise a default application menu (hidden from Tk) will be inserted into
the menubar at that time and subsequent addition of a .apple menu will no
longer result in it becoming the Application menu.
When Tk sees a .menubar.window menu on the Macintosh, the menu's
contents are inserted into the standard Window menu of the user's menubar
whenever the window's menubar is in front. The first items in the menu are
provided by Mac OS X, and the names of the current toplevels are
automatically appended after all the Tk-defined items and a separator.
When Tk sees a .menubar.help menu on the Macintosh, the menu's
contents are appended to the standard Help menu of the user's menubar
whenever the window's menubar is in front. The first items in the menu are
provided by Mac OS X.
When Tk sees a System menu on Windows, its items are appended to
the system menu that the menubar is attached to. This menu is tied to the
application icon and can be invoked with the mouse or by typing
Alt+Spacebar. Due to limitations in the Windows API, any font changes,
colors, images, bitmaps, or tearoff images will not appear in the system
menu.
When Tk sees a Help menu on X Windows and Motif menu compatibility
is enabled the menu is moved to be last in the menubar and is right
justified. Motif menu compatibility is enabled by setting the Tk option
*Menu.useMotifHelp to true or by calling tk::classic::restore
menu.
When a menu is set as a menubar for a toplevel window, or when a
menu is torn off, a clone of the menu is made. This clone is a menu widget
in its own right, but it is a child of the original. Changes in the
configuration of the original are reflected in the clone. Additionally, any
cascades that are pointed to are also cloned so that menu traversal will
work right. Clones are destroyed when either the tearoff or menubar goes
away, or when the original menu is destroyed.
The menu command creates a new Tcl command whose name is
pathName. This command may be used to invoke various operations on
the widget. It has the following general form:
pathName option ?arg arg ...?
Option and the args determine the exact behavior of the command.
Many of the widget commands for a menu take as one argument an
indicator of which entry of the menu to operate on. These indicators are
called indexes and may be specified in any of the following
forms:
- active
- Indicates the entry that is currently active. If no entry is active then
this form is equivalent to none. This form may not be
abbreviated.
- end
- Indicates the bottommost entry in the menu. If there are no entries in the
menu then this form is equivalent to none. This form may not be
abbreviated.
- last
- Same as end.
- none
- Indicates “no entry at all”; this is used most commonly with
the activate option to deactivate all the entries in the menu. In
most cases the specification of none causes nothing to happen in
the widget command. This form may not be abbreviated.
- @number
- In this form, number is treated as a y-coordinate in the menu's
window; the entry closest to that y-coordinate is used. For example,
“@0” indicates the top-most entry in the window.
- number
- Specifies the entry numerically, where 0 corresponds to the top-most entry
of the menu, 1 to the entry below it, and so on.
- pattern
- If the index does not satisfy one of the above forms then this form is
used. Pattern is pattern-matched against the label of each entry in
the menu, in order from the top down, until a matching entry is found. The
rules of string match are used.
If the index could match more than one of the above forms, then
the form earlier in the above list takes precedence.
The following widget commands are possible for menu widgets:
- pathName
activate index
- Change the state of the entry indicated by index to active
and redisplay it using its active colors. Any previously-active entry is
deactivated. If index is specified as none, or if the
specified entry is disabled, then the menu ends up with no active entry.
Returns an empty string.
- pathName
add type ?option value option value ...?
- Add a new entry to the bottom of the menu. The new entry's type is given
by type and must be one of cascade, checkbutton,
command, radiobutton, or separator, or a unique
abbreviation of one of the above. If additional arguments are present,
they specify the options listed in the MENU ENTRY OPTIONS section
below. The add widget command returns an empty string.
- pathName
cget option
- Returns the current value of the configuration option given by
option. Option may have any of the values accepted by the
menu command.
- pathName
clone newPathname ?cloneType?
- Makes a clone of the current menu named newPathName. This clone is
a menu in its own right, but any changes to the clone are propagated to
the original menu and vice versa. cloneType can be normal,
menubar, or tearoff. Should not normally be called outside
of the Tk library. See the CLONES section for more
information.
- pathName
configure ?option? ?value option value
...?
- Query or modify the configuration options of the widget. If no
option is specified, returns a list describing all of the available
options for pathName (see Tk_ConfigureInfo for information
on the format of this list). If option is specified with no
value, then the command returns a list describing the one named
option (this list will be identical to the corresponding sublist of the
value returned if no option is specified). If one or more
option-value pairs are specified, then the command modifies the
given widget option(s) to have the given value(s); in this case the
command returns an empty string. Option may have any of the values
accepted by the menu command.
- pathName
delete index1 ?index2?
- Delete all of the menu entries between index1 and index2
inclusive. If index2 is omitted then it defaults to index1.
Attempts to delete a tear-off menu entry are ignored (instead, you should
change the -tearoff option to remove the tear-off entry).
- pathName
entrycget index option
- Returns the current value of a configuration option for the entry given by
index. Option may have any of the names described in the
MENU ENTRY OPTIONS section below.
- pathName
entryconfigure index ?options...?
- This command is similar to the configure command, except that it
applies to the options for an individual entry, whereas configure
applies to the options for the menu as a whole. Options may have
any of the values described in the MENU ENTRY OPTIONS section
below. If options are specified, options are modified as indicated
in the command and the command returns an empty string. If no
options are specified, returns a list describing the current
options for entry index (see Tk_ConfigureInfo for
information on the format of this list).
- pathName
index index
- Returns the numerical index corresponding to index, or none
if index was specified as none.
- pathName
insert index type ?option value option value
...?
- Same as the add widget command except that it inserts the new entry
just before the entry given by index, instead of appending to the
end of the menu. The type, option, and value
arguments have the same interpretation as for the add widget
command. It is not possible to insert new menu entries before the tear-off
entry, if the menu has one.
- pathName
invoke index
- Invoke the action of the menu entry. See the sections on the individual
entries above for details on what happens. If the menu entry is disabled
then nothing happens. If the entry has a command associated with it then
the result of that command is returned as the result of the invoke
widget command. Otherwise the result is an empty string. Note: invoking a
menu entry does not automatically unpost the menu; the default bindings
normally take care of this before invoking the invoke widget
command.
- pathName
post x y
- Arrange for the menu to be displayed on the screen at the root-window
coordinates given by x and y. These coordinates are adjusted
if necessary to guarantee that the entire menu is visible on the screen.
This command normally returns an empty string. If the -postcommand
option has been specified, then its value is executed as a Tcl script
before posting the menu and the result of that script is returned as the
result of the post widget command. If an error returns while
executing the command, then the error is returned without posting the
menu.
- pathName
postcascade index
- Posts the submenu associated with the cascade entry given by index,
and unposts any previously posted submenu. If index does not
correspond to a cascade entry, or if pathName is not posted, the
command has no effect except to unpost any currently posted submenu.
- pathName
type index
- Returns the type of the menu entry given by index. This is the
type argument passed to the add or insert widget
command when the entry was created, such as command or
separator, or tearoff for a tear-off entry.
- pathName
unpost
- Unmap the window so that it is no longer displayed. If a lower-level
cascaded menu is posted, unpost that menu. Returns an empty string. This
subcommand does not work on Windows and the Macintosh, as those platforms
have their own way of unposting menus.
- pathName
xposition index
- Returns a decimal string giving the x-coordinate within the menu window of
the leftmost pixel in the entry specified by index.
- pathName
yposition index
- Returns a decimal string giving the y-coordinate within the menu window of
the topmost pixel in the entry specified by index.
The following options are allowed on menu entries. Most options
are not supported by all entry types.
- -activebackground
value
- Specifies a background color to use for displaying this entry when it is
active. If this option is specified as an empty string (the default), then
the -activebackground option for the overall menu is used. If the
tk_strictMotif variable has been set to request strict Motif
compliance, then this option is ignored and the -background option
is used in its place. This option is not available for separator or
tear-off entries.
- -activeforeground
value
- Specifies a foreground color to use for displaying this entry when it is
active. If this option is specified as an empty string (the default), then
the -activeforeground option for the overall menu is used. This
option is not available for separator or tear-off entries.
- -accelerator
value
- Specifies a string to display at the right side of the menu entry.
Normally describes an accelerator keystroke sequence that may be used to
invoke the same function as the menu entry. This is a display option, it
does not actually set the corresponding binding (which can be achieved
using the bind command). This option is not available for separator
or tear-off entries.
- -background
value
- Specifies a background color to use for displaying this entry when it is
in the normal state (neither active nor disabled). If this option is
specified as an empty string (the default), then the -background
option for the overall menu is used. This option is not available for
separator or tear-off entries.
- -bitmap
value
- Specifies a bitmap to display in the menu instead of a textual label, in
any of the forms accepted by Tk_GetBitmap. This option overrides
the -label option (as controlled by the -compound option)
but may be reset to an empty string to enable a textual label to be
displayed. If a -image option has been specified, it overrides
-bitmap. This option is not available for separator or tear-off
entries.
- -columnbreak
value
- When this option is zero, the entry appears below the previous entry. When
this option is one, the entry appears at the top of a new column in the
menu. This option is ignored on Aqua/Mac OS X, where menus are always a
single column.
- -command
value
- Specifies a Tcl command to execute when the menu entry is invoked. Not
available for separator or tear-off entries.
- -compound
value
- Specifies whether the menu entry should display both an image and text,
and if so, where the image should be placed relative to the text. Valid
values for this option are bottom, center, left,
none, right and top. The default value is
none, meaning that the button will display either an image or text,
depending on the values of the -image and -bitmap
options.
- -font
value
- Specifies the font to use when drawing the label or accelerator string in
this entry. If this option is specified as an empty string (the default)
then the -font option for the overall menu is used. This option is
not available for separator or tear-off entries.
- -foreground
value
- Specifies a foreground color to use for displaying this entry when it is
in the normal state (neither active nor disabled). If this option is
specified as an empty string (the default), then the -foreground
option for the overall menu is used. This option is not available for
separator or tear-off entries.
- -hidemargin
value
- Specifies whether the standard margins should be drawn for this menu
entry. This is useful when creating palette with images in them, i.e.,
color palettes, pattern palettes, etc. 1 indicates that the margin for the
entry is hidden; 0 means that the margin is used.
- -image
value
- Specifies an image to display in the menu instead of a text string or
bitmap. The image must have been created by some previous invocation of
image create. This option overrides the -label and
-bitmap options (as controlled by the -compound option) but
may be reset to an empty string to enable a textual or bitmap label to be
displayed. This option is not available for separator or tear-off
entries.
- -indicatoron
value
- Available only for checkbutton and radiobutton entries. Value is a
boolean that determines whether or not the indicator should be
displayed.
- -label
value
- Specifies a string to display as an identifying label in the menu entry.
Not available for separator or tear-off entries.
- Available only for cascade entries. Specifies the path name of the submenu
associated with this entry. The submenu must be a child of the menu.
- -offvalue
value
- Available only for checkbutton entries. Specifies the value to store in
the entry's associated variable when the entry is deselected.
- -onvalue
value
- Available only for checkbutton entries. Specifies the value to store in
the entry's associated variable when the entry is selected.
- -selectcolor
value
- Available only for checkbutton and radiobutton entries. Specifies the
color to display in the indicator when the entry is selected. If the value
is an empty string (the default) then the -selectcolor option for
the menu determines the indicator color.
- -selectimage
value
- Available only for checkbutton and radiobutton entries. Specifies an image
to display in the entry (in place of the -image option) when it is
selected. Value is the name of an image, which must have been
created by some previous invocation of image create. This option is
ignored unless the -image option has been specified.
- -state
value
- Specifies one of three states for the entry: normal, active,
or disabled. In normal state the entry is displayed using the
-foreground option for the menu and the -background option
from the entry or the menu. The active state is typically used when the
pointer is over the entry. In active state the entry is displayed using
the -activeforeground option for the menu along with the
-activebackground option from the entry. Disabled state means that
the entry should be insensitive: the default bindings will refuse to
activate or invoke the entry. In this state the entry is displayed
according to the -disabledforeground option for the menu and the
-background option from the entry. This option is not available for
separator entries.
- -underline
value
- Specifies the integer index of a character to underline in the entry. This
option is also queried by the default bindings and used to implement
keyboard traversal. 0 corresponds to the first character of the text
displayed in the entry, 1 to the next character, and so on. If a bitmap or
image is displayed in the entry then this option is ignored. This option
is not available for separator or tear-off entries.
- -value
value
- Available only for radiobutton entries. Specifies the value to store in
the entry's associated variable when the entry is selected. If an empty
string is specified, then the -label option for the entry as the
value to store in the variable.
- -variable
value
- Available only for checkbutton and radiobutton entries. Specifies the name
of a global variable to set when the entry is selected. For checkbutton
entries the variable is also set when the entry is deselected. For
radiobutton entries, changing the variable causes the currently-selected
entry to deselect itself.
For checkbutton entries, the default value of this option is taken
from the -label option, and for radiobutton entries a single fixed
value is used. It is recommended that you always set the -variable
option when creating either a checkbutton or a radiobutton.
The default bindings support four different ways of using
menus:
- Pulldown Menus in
Menubar
- This is the most common case. You create a menu widget that will become
the menu bar. You then add cascade entries to this menu, specifying the
pull down menus you wish to use in your menu bar. You then create all of
the pulldowns. Once you have done this, specify the menu using the
-menu option of the toplevel's widget command. See the
toplevel manual entry for details.
- Pulldown Menus
in Menu Buttons
- This is the compatible way to do menu bars. You create one menubutton
widget for each top-level menu, and typically you arrange a series of
menubuttons in a row in a menubar window. You also create the top-level
menus and any cascaded submenus, and tie them together with -menu
options in menubuttons and cascade menu entries. The top-level menu must
be a child of the menubutton, and each submenu must be a child of the menu
that refers to it. Once you have done this, the default bindings will
allow users to traverse and invoke the tree of menus via its menubutton;
see the menubutton manual entry for details.
- Popup menus typically post in response to a mouse button press or
keystroke. You create the popup menus and any cascaded submenus, then you
call the tk_popup procedure at the appropriate time to post the
top-level menu.
- Option
Menus
- An option menu consists of a menubutton with an associated menu that
allows you to select one of several values. The current value is displayed
in the menubutton and is also stored in a global variable. Use the
tk_optionMenu procedure to create option menubuttons and their
menus.
- Torn-off
Menus
- You create a torn-off menu by invoking the tear-off entry at the top of an
existing menu. The default bindings will create a new menu that is a copy
of the original menu and leave it permanently posted as a top-level
window. The torn-off menu behaves just the same as the original menu.
Tk automatically creates class bindings for menus that give them
the following default behavior:
- [1]
- When the mouse enters a menu, the entry underneath the mouse cursor
activates; as the mouse moves around the menu, the active entry changes to
track the mouse.
- [2]
- When the mouse leaves a menu all of the entries in the menu deactivate,
except in the special case where the mouse moves from a menu to a cascaded
submenu.
- [3]
- When a button is released over a menu, the active entry (if any) is
invoked. The menu also unposts unless it is a torn-off menu.
- [4]
- The Space and Return keys invoke the active entry and unpost the
menu.
- [5]
- If any of the entries in a menu have letters underlined with the
-underline option, then pressing one of the underlined letters (or
its upper-case or lower-case equivalent) invokes that entry and unposts
the menu.
- [6]
- The Escape key aborts a menu selection in progress without invoking any
entry. It also unposts the menu unless it is a torn-off menu.
- [7]
- The Up and Down keys activate the next higher or lower entry in the menu.
When one end of the menu is reached, the active entry wraps around to the
other end.
- [8]
- The Left key moves to the next menu to the left. If the current menu is a
cascaded submenu, then the submenu is unposted and the current menu entry
becomes the cascade entry in the parent. If the current menu is a
top-level menu posted from a menubutton, then the current menubutton is
unposted and the next menubutton to the left is posted. Otherwise the key
has no effect. The left-right order of menubuttons is determined by their
stacking order: Tk assumes that the lowest menubutton (which by default is
the first one created) is on the left.
- [9]
- The Right key moves to the next menu to the right. If the current entry is
a cascade entry, then the submenu is posted and the current menu entry
becomes the first entry in the submenu. Otherwise, if the current menu was
posted from a menubutton, then the current menubutton is unposted and the
next menubutton to the right is posted.
Disabled menu entries are non-responsive: they do not activate and
they ignore mouse button presses and releases.
Several of the bindings make use of the command
tk_menuSetFocus. It saves the current focus and sets the focus to its
pathName argument, which is a menu widget.
The behavior of menus can be changed by defining new bindings for
individual widgets or by redefining the class bindings.
At present it is not possible to use the option database to
specify values for the options to individual entries.