perl-tk 1:804.031-1build1 / usr / lib / perl5 / Tk / Menu.pod

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#  Copyright (c) 1994-1997 Sun Microsystems, Inc.
#  See the file "license.terms" for information on usage and redistribution
#  of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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=head1 NAME

Tk::Menu - Create and manipulate Menu widgets

=for category  Tk Widget Classes

=head1 SYNOPSIS

S<    >I<$menu> = I<$parent>-E<gt>B<Menu>(?I<options>?);

=head1 STANDARD OPTIONS

B<-activebackground>	B<-background>	B<-disabledforeground>	B<-relief>
B<-activeborderwidth>	B<-borderwidth>	B<-font>	B<-takefocus>
B<-activeforeground>	B<-cursor>	B<-foreground>

See L<Tk::options> for details of the standard options.

=head1 WIDGET-SPECIFIC OPTIONS

=over 4

=item Name:	B<postCommand>

=item Class:	B<Command>

=item Switch:	B<-postcommand>

If this option is specified then it provides a L<callback|Tk::callbacks> to execute
each time the menu is posted.  The callback is invoked by the B<post>
method before posting the menu. Note that in 8.0 on Macintosh
and Windows, all commands in a menu systems are executed before any
are posted. This is due to the limitations in the individual platforms'
menu managers.

=item Name:	B<selectColor>

=item Class:	B<Background>

=item Switch:	B<-selectcolor>

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.

=item Name:	B<tearOff>

=item Class:	B<TearOff>

=item Switch:	B<-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.

=item Name:	B<tearOffCommand>

=item Class:	B<TearOffCommand>

=item Switch:	B<-tearoffcommand>

If this option has a non-empty value, then it specifies a L<perl/Tk callback|Tk::callbacks>
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 is ``B<a b>'' and menu B<.x.y> is torn off to
create a new menu B<.x.tearoff1>, then the command
``B<a b .x.y .x.tearoff1>'' will be invoked.

=item Name:	B<title>

=item Class:	B<Title>

=item Switch:	B<-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.

=item Name:	B<type>

=item Class:	B<Type>

=item Switch:	B<-type>

This option can be one of B<menubar>, B<tearoff>, or
B<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.

=back

=head1 DESCRIPTION

The B<Menu> method creates a new top-level window (given
by the $widget argument) and makes it into a menu widget.
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 B<menu> command returns its
$widget argument.  At the time this command is invoked,
there must not exist a window named $widget, but
$widget'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 B<-label>,
B<-bitmap>, and B<-image> options for the entry.
If the  B<-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 typed in the
application to cause the same result as invoking the menu entry.
The third field is an I<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 I<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 I<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 E<lt>E<lt>MenuSelectE<gt>E<gt> virtual
event is sent 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.

=head2 COMMAND ENTRIES

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 callback is executed.  The callback
is specified with the B<-command> option.

=head2 SEPARATOR ENTRIES

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.

=head2 CHECKBUTTON ENTRIES

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 B<-onvalue> and B<-variable> options for the entry);  when
the entry is deselected another value (determined by the
B<-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 B<-selectcolor> option for the entry;
otherwise the indicator's center is displayed in the background color for
the menu.  If a B<-command> option is specified for a checkbutton
entry, then its value is evaluated each time the entry
is invoked;  this happens after toggling the entry's
selected state.

=head2 RADIOBUTTON ENTRIES

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 B<-value> and
B<-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 B<-selectcolor> option
for the entry;
otherwise the indicator's center is displayed in the background color for
the menu.  If a B<-command> option is specified for a radiobutton
entry, then its value is evaluated each time the entry
is invoked;  this happens after selecting the entry.

=head2 CASCADE ENTRIES

A cascade entry is one with an associated menu (determined
by the B<-menu> option).  Cascade entries allow the construction
of cascading menus.
The B<postcascade> method 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

=over 4

I<$menu>-E<gt>B<post>(I<x,y>)

=back

where I<menu> is the path name of the associated menu, and I<x>
and I<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

=over 4

I<$menu>-E<gt>B<unpost>

=back

where I<menu> is the name of the associated menu.
On other platforms, the platform's native code takes care of unposting the
menu.

If a B<-command> option is specified for a cascade entry then it is
evaluated whenever the entry is invoked. This is not supported on Windows.

=head2 TEAR-OFF ENTRIES

A tear-off entry appears at the top of the menu if enabled with the
B<tearOff> option.  It is not like other menu entries in that
it cannot be created with the B<add> method and
cannot be deleted with the B<delete> method.
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.

=head2 MENUBARS

Any menu can be set as a menubar for a toplevel window (see the
L<Toplevel|Tk::Toplevel> constructor 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 accross 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 L<"CLONES"> 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.

=head2 SPECIAL MENUS IN MENUBARS

Certain menus in a menubar will be treated specially.  On the Macintosh,
access to the special Apple 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 is provided. 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 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 an Apple menu on the Macintosh, that menu's contents make
up the first items of the Apple menu on the screen whenever the window
containing the menubar is in front. The menu is the
first one that the user sees and has a title which is an Apple logo.
After all of the Tk-defined items, the menu will have a separator,
followed by all of the items in the user's Apple Menu Items folder.
Since the System uses a different menu definition procedure for
the Apple menu than Tk uses for its menus, and the system APIs do
not fully support everything Tk tries to do, the menu item will only
have its text displayed. No font attributes, images, bitmaps, or colors
will be displayed. In addition, a menu with a tearoff item will have
the tearoff item displayed as "(TearOff)".

When Tk see a Help menu on the Macintosh, the menu's contents are
appended to the standard help menu on the right of the user's menubar
whenever the user's menubar is in front. The first items in the menu
are provided by Apple. Similar to the Apple Menu, cusomization in this
menu is limited to what the system provides.

When Tk sees a System menu on Windows, its items are appended to the
system menu that the menubar is attached to. This menu has an icon
representing a spacebar, 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 see a Help menu on X Windows, the menu is moved to be last in
the menubar and is right justified.

=head2 CLONES

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.

=head2 WIDGET METHODS

The B<Menu> method creates a widget object.
This object supports the B<configure> and B<cget> methods
described in L<Tk::options> which can be used to enquire and
modify the options described above.
The widget also inherits all the methods provided by the generic
L<Tk::Widget|Tk::Widget> class, and the L<Tk::Wm|Tk::Wm> class.

Many of the methods for a menu take as one argument an
indicator of which entry of the menu to operate on.  These
indicators are called I<index>es and may be specified in
any of the following forms:

=over 4

=item I<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.

=item B<active>

Indicates the entry that is currently active.  If no entry is
active then this form is equivalent to B<none>.  This form may
not be abbreviated.

=item B<end>

Indicates the bottommost entry in the menu.  If there are no
entries in the menu then this form is equivalent to B<none>.
This form may not be abbreviated.

=item B<last>

Same as B<end>.

=item B<none>

Indicates ``no entry at all'';  this is used most commonly with
the B<activate> option to deactivate all the entries in the
menu.  In most cases the specification of B<none> causes
nothing to happen in the method.
This form may not be abbreviated.

=item B<@>I<number>

In this form, I<number> is treated as a y-coordinate in the
menu's window;  the entry closest to that y-coordinate is used.
For example, ``B<@0>'' indicates the top-most entry in the
window.

=item I<pattern>

If the index doesn't satisfy one of the above forms then this
form is used.  I<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.
(In perl/Tk the matching is under review, but exact match
should work.)

=back

The following methods are possible for menu widgets:

=over 4

=item I<$menu>-E<gt>B<activate>(I<index>)

Change the state of the entry indicated by I<index> to B<active>
and redisplay it using its active colors.
Any previously-active entry is deactivated.  If I<index>
is specified as B<none>, or if the specified entry is
disabled, then the menu ends up with no active entry.
Returns an empty string.

=item I<$menu>-E<gt>B<add>(I<type, >?I<option, value, option, value, ...>?)

Add a new entry to the bottom of the menu.  The new entry's type
is given by I<type> and must be one of B<cascade>,
B<checkbutton>, B<command>, B<radiobutton>, or B<separator>,
or a unique abbreviation of one of the above.  If additional arguments
are present, they specify any of the following options:

=over 8

=item B<-activebackground> =E<gt> I<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
B<activeBackground> option for the overall menu is used.
If the B<$Tk::strictMotif> variable has been set to request strict
Motif compliance, then this option is ignored and the B<-background>
option is used in its place.
This option is not available for separator or tear-off entries.

=item B<-activeforeground> =E<gt> I<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
B<activeForeground> option for the overall menu is used.
This option is not available for separator or tear-off entries.

=item B<-accelerator> =E<gt> I<value>

Specifies a string to display at the right side of the menu entry.
Normally describes an accelerator keystroke sequence that may be
typed to invoke the same function as the menu entry.  This option
is not available for separator or tear-off entries.

=item B<-background> =E<gt> I<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
B<background> option for the overall menu is used.
This option is not available for separator or tear-off entries.

=item B<-bitmap> =E<gt> I<value>

Specifies a bitmap to display in the menu instead of a textual
label, in any of the forms accepted by B<Tk_GetBitmap>.
This option overrides the B<-label> option but may be reset
to an empty string to enable a textual label to be displayed.
If a B<-image> option has been specified, it overrides
B<-bitmap>.
This option is not available for separator or tear-off entries.

=item B<-columnbreak> =E<gt> I<value>

When this option is zero, the appears below the previous entry. When
this option is one, the menu appears at the top of a new column in the
menu.

=item B<-compound> =E<gt> I<value>

Specifies whether the button 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 B<bottom>, B<center>, B<left>,
B<none>, B<right> and B<top>.  The default value is B<none>, meaning
that the button will display either an image or text, depending on the
values of the -image and -bitmap options.

=item B<-command> =E<gt> I<value>

For command, checkbutton, and radiobutton entries, specifies a
callback to execute when the menu entry is invoked.
For cascade entries, specifies a callback to execute
when the entry is activated (i.e. just before its submenu is
posted).
Not available for separator or tear-off entries.

=item B<-font> =E<gt> I<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 B<font> option for the overall menu is used.
This option is not available for separator or tear-off entries.

=item B<-foreground> =E<gt> I<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
B<foreground> option for the overall menu is used.
This option is not available for separator or tear-off entries.

=item B<-hidemargin> =E<gt> I<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.

=item B<-image> =E<gt> I<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
B<image create>.
This option overrides the B<-label> and B<-bitmap> options
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.

=item B<-indicatoron> =E<gt> I<value>

Available only for checkbutton and radiobutton entries.
I<Value> is a boolean that determines whether or not the
indicator should be displayed.

=item B<-label> =E<gt> I<value>

Specifies a string to display as an identifying label in the menu
entry.  Not available for separator or tear-off entries.

=item B<-menu> =E<gt> I<value>

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.

=item B<-offvalue> =E<gt> I<value>

Available only for checkbutton entries.  Specifies the value to
store in the entry's associated variable when the entry is
deselected.

=item B<-onvalue> =E<gt> I<value>

Available only for checkbutton entries.  Specifies the value to
store in the entry's associated variable when the entry is selected.

=item B<-selectcolor> =E<gt> I<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 B<selectColor>
option for the menu determines the indicator color.

=item B<-selectimage> =E<gt> I<value>

Available only for checkbutton and radiobutton entries.
Specifies an image to display in the entry (in place of
the B<-image> option) when it is selected.
I<Value> is the name of an image, which must have been created
by some previous invocation of B<image create>.
This option is ignored unless the B<-image> option has
been specified.

=item B<-state> =E<gt> I<value>

Specifies one of three states for the entry:  B<normal>, B<active>,
or B<disabled>.  In normal state the entry is displayed using the
B<foreground> option for the menu and the B<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 B<activeForeground>
option for the menu along with the B<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
B<disabledForeground> option for the menu and the
B<background> option from the entry.
This option is not available for separator entries.

=item B<-underline> =E<gt> I<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.

=item B<-value> =E<gt> I<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 B<-label> option
for the entry as the value to store in the variable.

=item B<-variable> =E<gt> I<value>

Available only for checkbutton and radiobutton entries.  Specifies
the name of a global value 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.

=back

The B<add> method returns an empty string.

=item I<$menu>-E<gt>B<clone>(I<$parent> ?, I<cloneType?>)

Makes a clone of the current menu as a child of I<$parent>. This clone
is a menu in its own right, but any changes to the clone are
propogated to the original menu and vice versa. I<cloneType> can be
B<normal>, B<menubar>, or B<tearoff>. Should not normally be
called outside of the Tk library. See L<"CLONES"> for
more information.

=item I<$menu>-E<gt>B<delete>(I<index1>?, I<index2>?)

Delete all of the menu entries between I<index1> and
I<index2> inclusive.
If I<index2> is omitted then it defaults to I<index1>.
Attempts to delete a tear-off menu entry are ignored (instead, you
should change the B<tearOff> option to remove the tear-off entry).

=item I<$menu>-E<gt>B<entrycget>(I<index, option>)

Returns the current value of a configuration option for
the entry given by I<index>.
I<Option> may have any of the values accepted by the B<add>
method.

=item I<$menu>-E<gt>B<entryconfigure>(I<index> ?,I<options>?)

This method is similar to the B<configure> method, except that
it applies to the options for an individual entry, whereas B<configure>
applies to the options for the menu as a whole.
I<Options> may have any of the values accepted by the B<add>
method.  If I<options> are specified, options are modified
as indicated
in the method call and the method returns an empty string.
If no I<options> are specified, returns a list describing
the current options for entry I<index> (see L<Tk::options> for
information on the format of this list).

=item I<$menu>-E<gt>B<index>(I<index>)

Returns the numerical index corresponding to I<index>, or
B<none> if I<index> was specified as B<none>.

=item I<$menu>-E<gt>B<insert>(I<index, type>?, I<-option>=E<gt>I<value>, ...?)

Same as the B<add> method except that it inserts the new
entry just before the entry given by I<index>, instead of appending
to the end of the menu.  The I<type>, I<-option>, and I<value>
arguments have the same interpretation as for the B<add> widget
method.  It is not possible to insert new menu entries before the
tear-off entry, if the menu has one.

=item I<$menu>-E<gt>B<invoke>(I<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 callback associated with it then the result of that
callback is returned as the result of the B<invoke> widget
method.  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 B<invoke>
method.

=item I<$menu>-E<gt>B<post>(I<x, y>)

Arrange for the menu to be displayed on the screen at the root-window
coordinates given by I<x> and I<y>.  These coordinates are
adjusted if necessary to guarantee that the entire menu is visible on
the screen.  This method normally returns an empty string.
If the B<postCommand> option has been specified, then its value is
executed before posting the menu and the result of
that callback is returned as the result of the B<post> widget
method.
If an error returns while executing the method, then the error is
returned without posting the menu.

=item I<$menu>-E<gt>B<postcascade>(I<index>)

Posts the submenu associated with the cascade entry given by
I<index>, and unposts any previously posted submenu.
If I<index> doesn't correspond to a cascade entry,
or if I<$menu> isn't posted,
the method has no effect except to unpost any currently posted
submenu.

=item I<$menu>-E<gt>B<type>(I<index>)

Returns the type of the menu entry given by I<index>.
This is the I<type> argument passed to the B<add> widget
method when the entry was created, such as B<command>
or B<separator>, or B<tearoff> for a tear-off entry.

=item I<$menu>-E<gt>B<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 method does not work on Windows and the
Macintosh, as those platforms have their own way of unposting menus.

=item I<$menu>-E<gt>B<yposition>(I<index>)

Returns a decimal string giving the y-coordinate within the menu
window of the topmost pixel in the entry specified by I<index>.

=back

=head1 MENU CONFIGURATIONS

The default bindings support four different ways of using menus:

=over 4

=item B<Pulldown Menus in Menubar>

This is the most command 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
B<-menu> option of the toplevel's method. See the
B<toplevel> manual entry for details.

=item B<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 B<-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 B<menubutton> documentation for details.

=item B<Popup Menus>

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 B<Post> method at the appropriate time
to post the top-level menu.

I<$menu>-E<gt>B<Post>(I<$x>,I<$y>?,I<$entry>?)

I<$x> and I<$y> are the root window coordinates at which the I<$menu>
will be displayed. If I<$entry> is specified then that entry is centred
on that point, otherwise the top-left corner of the I<$menu> is placed
at that point.

B<Menu> also inherits methods from L<Tk::Wm> and so the method
B<Popup> can be used to position menu relative to other windows, the
mouse cursor or the screen.

=item B<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 L<Tk::Optionmenu> class to create option
menubuttons and their menus.

=item B<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.

=back

=head1 DEFAULT BINDINGS

Tk automatically creates class bindings for menus that give them
the following default behavior:

=over 4

=item [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.

=item [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.

=item [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.

=item [4]

The Space and Return keys invoke the active entry and
unpost the menu.

=item [5]

If any of the entries in a menu have letters underlined with
with B<-underline> option, then pressing one of the underlined
letters (or its upper-case or lower-case equivalent) invokes that
entry and unposts the menu.

=item [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.

=item [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.

=item [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.

=item [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 don't activate and
they ignore mouse button presses and releases.

The behavior of menus can be changed by defining new bindings for
individual widgets or by redefining the class bindings.

=back

=head1 BUGS

At present it isn't possible to use the
option database to specify values for the options to individual
entries.

=head1 SEE ALSO

L<Tk::callbacks|Tk::callbacks>

=head1 KEYWORDS

menu, widget

=cut