Provided by: tk8.6-doc_8.6.12-1build1_all bug


       bind - Arrange for X events to invoke Tcl scripts


       bind tag ?sequence? ?+??script?


       The  bind  command  associates  Tcl  scripts  with  X  events.  If all three arguments are
       specified, bind will arrange for script (a Tcl script called the “binding script”)  to  be
       evaluated  whenever  the  event(s)  given by sequence occur in the window(s) identified by
       tag.  If script is prefixed with a “+”, then it is appended to any  existing  binding  for
       sequence;   otherwise  script replaces any existing binding.  If script is an empty string
       then the current binding for sequence is destroyed, leaving sequence unbound.  In  all  of
       the cases where a script argument is provided, bind returns an empty string.

       If  sequence is specified without a script, then the script currently bound to sequence is
       returned, or an empty string is returned if there is no binding for sequence.  If  neither
       sequence  nor  script is specified, then the return value is a list whose elements are all
       the sequences for which there exist bindings for tag.

       The tag argument determines which window(s) the binding applies to.  If tag begins with  a
       dot,  as  in  .a.b.c,  then  it must be the path name for a window; otherwise it may be an
       arbitrary string.  Each window has an associated list of tags, and a binding applies to  a
       particular  window  if  its  tag  is  among  those specified for the window.  Although the
       bindtags command may be used to assign an arbitrary set of binding tags to a  window,  the
       default binding tags provide the following behavior:

       •  If a tag is the name of an internal window the binding applies to that window.

       •  If  the tag is the name of a toplevel window the binding applies to the toplevel window
          and all its internal windows.

       •  If the tag is the name of a class of widgets, such as Button, the  binding  applies  to
          all widgets in that class;

       •  If tag has the value all, the binding applies to all windows in the application.


       The  sequence  argument  specifies a sequence of one or more event patterns, with optional
       white space between the patterns.  Each event pattern may take one of three forms.  In the
       simplest  case it is a single printing ASCII character, such as a or [.  The character may
       not be a space character or the character <.  This form  of  pattern  matches  a  KeyPress
       event  for  the  particular  character.   The  second  form  of pattern is longer but more
       general.  It has the following syntax:
       The entire event pattern is surrounded by angle brackets.  Inside the angle  brackets  are
       zero  or  more  modifiers,  an  event  type,  and  an  extra piece of information (detail)
       identifying a particular button or keysym.  Any of the fields may be omitted, as  long  as
       at  least  one of type and detail is present.  The fields must be separated by white space
       or dashes.

       The third form of pattern is used to specify a user-defined, named virtual event.  It  has
       the following syntax:
       The entire virtual event pattern is surrounded by double angle brackets.  Inside the angle
       brackets is the user-defined name of the virtual  event.   Modifiers,  such  as  Shift  or
       Control,  may  not  be  combined with a virtual event to modify it.  Bindings on a virtual
       event may be created before the virtual event is defined,  and  if  the  definition  of  a
       virtual  event  changes  dynamically, all windows bound to that virtual event will respond
       immediately to the new definition.

       Some widgets (e.g. menu and text) issue  virtual  events  when  their  internal  state  is
       updated in some ways.  Please see the manual page for each widget for details.

       Modifiers consist of any of the following values:

              Control                 Mod1, M1, Command
              Alt                     Mod2, M2, Option
              Shift                   Mod3, M3
              Lock                    Mod4, M4
              Extended                Mod5, M5
              Button1, B1             Meta, M
              Button2, B2             Double
              Button3, B3             Triple
              Button4, B4             Quadruple
              Button5, B5

       Where more than one value is listed, separated by commas, the values are equivalent.  Most
       of the modifiers have the obvious X meanings.  For example, Button1 requires that button 1
       be  depressed  when the event occurs.  For a binding to match a given event, the modifiers
       in the event must include all of those specified in the event pattern.  An event may  also
       contain  additional  modifiers  not specified in the binding.  For example, if button 1 is
       pressed while the shift and control keys are down,  the  pattern  <Control-Button-1>  will
       match  the  event,  but <Mod1-Button-1> will not.  If no modifiers are specified, then any
       combination of modifiers may be present in the event.

       Meta and M refer to whichever of the M1 through M5 modifiers is associated with  the  Meta
       key(s) on the keyboard (keysyms Meta_R and Meta_L).  If there are no Meta keys, or if they
       are not associated with any modifiers,  then  Meta  and  M  will  not  match  any  events.
       Similarly, the Alt modifier refers to whichever modifier is associated with the alt key(s)
       on the keyboard (keysyms Alt_L and Alt_R).

       The Double, Triple and Quadruple modifiers are a convenience for specifying  double  mouse
       clicks  and other repeated events. They cause a particular event pattern to be repeated 2,
       3 or 4 times, and also place a time and space requirement on the sequence: for a  sequence
       of  events  to  match  a Double, Triple or Quadruple pattern, all of the events must occur
       close together in time and without substantial mouse  motion  in  between.   For  example,
       <Double-Button-1>  is  equivalent  to  <Button-1><Button-1>  with the extra time and space

       The Command and Option modifiers are equivalents of Mod1 resp. Mod2,  they  correspond  to
       Macintosh-specific modifier keys.

       The  Extended modifier is, at present, specific to Windows.  It appears on events that are
       associated with the keys on the “extended keyboard”.  On a US keyboard, the extended  keys
       include  the  Alt  and  Control  keys at the right of the keyboard, the cursor keys in the
       cluster to the left of the numeric pad, the NumLock key, the Break  key,  the  PrintScreen
       key, and the / and Enter keys in the numeric keypad.

       The  type  field may be any of the standard X event types, with a few extra abbreviations.
       The type field will also accept a couple non-standard X event types  that  were  added  to
       better  support  the  Macintosh  and  Windows platforms.  Below is a list of all the valid
       types; where two names appear together, they are synonyms.

              Activate              Destroy         Map
              ButtonPress, Button   Enter           MapRequest
              ButtonRelease         Expose          Motion
              Circulate             FocusIn         MouseWheel
              CirculateRequest      FocusOut        Property
              Colormap              Gravity         Reparent
              Configure             KeyPress, Key   ResizeRequest
              ConfigureRequest      KeyRelease      Unmap
              Create                Leave           Visibility

       Most of the above events have the same fields and behaviors as events in the  X  Windowing
       system.   You  can  find  more  detailed  descriptions  of  these  events  in any X window
       programming book.  A couple of the events are extensions to the X event system to  support
       features  unique  to the Macintosh and Windows platforms.  We provide a little more detail
       on these events here.  These include:

       Activate, Deactivate
            These two events are sent to every sub-window of a toplevel when they  change  state.
            In  addition to the focus Window, the Macintosh platform and Windows platforms have a
            notion of an active window (which often has but is not required to have  the  focus).
            On  the  Macintosh,  widgets  in  the  active window have a different appearance than
            widgets in deactive windows.  The Activate event is sent to all the sub-windows in  a
            toplevel when it changes from being deactive to active.  Likewise, the Deactive event
            is sent when the window's state changes from active to deactive.  There are no useful
            percent substitutions you would make when binding to these events.

            Many  contemporary  mice support a mouse wheel, which is used for scrolling documents
            without using the scrollbars.   By  rolling  the  wheel,  the  system  will  generate
            MouseWheel events that the application can use to scroll.  The event is routed to the
            window currently under the mouse pointer. When the event is received you can use  the
            %D  substitution  to  get  the  delta  field for the event, which is an integer value
            describing how the mouse wheel has moved.  The smallest value for  which  the  system
            will  report  is defined by the OS.  The sign of the value determines which direction
            your widget should scroll.  Positive values should  scroll  up  and  negative  values
            should scroll down.

            Horizontal   scrolling   uses   Shift-MouseWheel   events,  with  positive  %D  delta
            substitution indicating left scrolling and negative right  scrolling.   Only  Windows
            and  macOS  Aqua  typically  fire  MouseWheel  and  Shift-MouseWheel  events.  On X11
            vertical scrolling is rather supported through  Button-4  and  Button-5  events,  and
            horizontal  scrolling  through  Shift-Button-4 and Shift-Button-5 events.  Horizontal
            scrolling events may fire from many different hardware units such as tilt  wheels  or
            touchpads.   Horizontal scrolling can also be emulated by holding Shift and scrolling

       KeyPress, KeyRelease
            The KeyPress and KeyRelease events  are  generated  whenever  a  key  is  pressed  or
            released.   KeyPress and KeyRelease events are sent to the window which currently has
            the keyboard focus.

       ButtonPress, ButtonRelease, Motion
            The ButtonPress and ButtonRelease events are  generated  when  the  user  presses  or
            releases  a mouse button.  Motion events are generated whenever the pointer is moved.
            ButtonPress, ButtonRelease, and  Motion  events  are  normally  sent  to  the  window
            containing the pointer.

            When  a  mouse  button  is  pressed,  the window containing the pointer automatically
            obtains a temporary pointer grab.  Subsequent ButtonPress, ButtonRelease, and  Motion
            events  will be sent to that window, regardless of which window contains the pointer,
            until all buttons have been released.

            A Configure event is sent to a window whenever its size, position,  or  border  width
            changes, and sometimes when it has changed position in the stacking order.

       Map, Unmap
            The  Map  and  Unmap  events  are  generated  whenever  the mapping state of a window

            Windows are created in the unmapped state.  Top-level windows become mapped when they
            transition  to the normal state, and are unmapped in the withdrawn and iconic states.
            Other windows become mapped when they are placed under control of a geometry  manager
            (for example pack or grid).

            A  window  is  viewable  only  if  it and all of its ancestors are mapped.  Note that
            geometry managers typically do not map their children until  they  have  been  mapped
            themselves,  and  unmap  all  children when they become unmapped; hence in Tk Map and
            Unmap events indicate whether or not a window is viewable.

            A window is said to be obscured when another window above it in  the  stacking  order
            fully  or partially overlaps it.  Visibility events are generated whenever a window's
            obscurity state changes; the state field (%s) specifies the new state.

            An Expose event is generated whenever all or part of a window should be redrawn  (for
            example,  when a window is first mapped or if it becomes unobscured).  It is normally
            not necessary for client applications to handle Expose events, since Tk handles  them

            A Destroy event is delivered to a window when it is destroyed.

            When  the  Destroy  event is delivered to a widget, it is in a “half-dead” state: the
            widget still exists, but operations that involve it may return  invalid  results,  or
            return an error.

       FocusIn, FocusOut
            The FocusIn and FocusOut events are generated whenever the keyboard focus changes.  A
            FocusOut event is sent to the old focus window, and a FocusIn event is  sent  to  the
            new one.

            In  addition, if the old and new focus windows do not share a common parent, “virtual
            crossing” focus events are sent to the intermediate windows in the hierarchy.  Thus a
            FocusIn event indicates that the target window or one of its descendants has acquired
            the focus, and a FocusOut event indicates that the focus has been changed to a window
            outside the target window's hierarchy.

            The keyboard focus may be changed explicitly by a call to focus, or implicitly by the
            window manager.

       Enter, Leave
            An Enter event is sent to a window when the pointer enters that window, and  a  Leave
            event is sent when the pointer leaves it.

            If  there  is  a pointer grab in effect, Enter and Leave events are only delivered to
            the window owning the grab.

            In addition, when the pointer moves between two windows,  Enter  and  Leave  “virtual
            crossing” events are sent to intermediate windows in the hierarchy in the same manner
            as for FocusIn and FocusOut events.

            A Property event is sent to a window whenever an X property belonging to that  window
            is changed or deleted.  Property events are not normally delivered to Tk applications
            as they are handled by the Tk core.

            A Colormap event is generated whenever the colormap associated with a window has been
            changed, installed, or uninstalled.

            Widgets  may  be  assigned  a  private colormap by specifying a -colormap option; the
            window manager is responsible for installing and uninstalling colormaps as necessary.

            Note that Tk provides no useful details for this event type.

       MapRequest, CirculateRequest, ResizeRequest, ConfigureRequest, Create
            These events are not normally delivered to Tk applications.  They  are  included  for
            completeness,  to make it possible to write X11 window managers in Tk.  (These events
            are only delivered when a client has selected SubstructureRedirectMask on  a  window;
            the Tk core does not use this mask.)

       Gravity, Reparent, Circulate
            The  events Gravity and Reparent are not normally delivered to Tk applications.  They
            are included for completeness.

            A Circulate event indicates that the window has moved to the top or to the bottom  of
            the  stacking  order  as  a result of an XCirculateSubwindows protocol request.  Note
            that the stacking order may be changed for other reasons  which  do  not  generate  a
            Circulate  event,  and  that Tk does not use XCirculateSubwindows() internally.  This
            event type is included only for completeness; there  is  no  reliable  way  to  track
            changes to a window's position in the stacking order.

       The  last  part  of a long event specification is detail.  In the case of a ButtonPress or
       ButtonRelease event, it is the number of a button (1-5).  If a  button  number  is  given,
       then  only  an  event on that particular button will match;  if no button number is given,
       then an event on any button will  match.   Note:   giving  a  specific  button  number  is
       different  than  specifying  a  button  modifier; in the first case, it refers to a button
       being pressed or released, while in the second it refers to  some  other  button  that  is
       already  depressed  when the matching event occurs.  If a button number is given then type
       may be omitted:  if will default to  ButtonPress.   For  example,  the  specifier  <1>  is
       equivalent to <ButtonPress-1>.

       If  the  event type is KeyPress or KeyRelease, then detail may be specified in the form of
       an X keysym.  Keysyms are textual specifications for particular keys on the keyboard; they
       include  all  the  alphanumeric  ASCII  characters  (e.g.  “a” is the keysym for the ASCII
       character “a”), plus descriptions for non-alphanumeric characters  (“comma”is  the  keysym
       for  the  comma  character),  plus descriptions for all the non-ASCII keys on the keyboard
       (e.g.  “Shift_L” is the keysym for the left shift key, and “F1” is the keysym for  the  F1
       function  key,  if it exists).  The complete list of keysyms is not presented here;  it is
       available in other X documentation and may vary from system to system.  If necessary,  you
       can use the %K notation described below to print out the keysym name for a particular key.
       If a keysym detail is given, then the type field may  be  omitted;   it  will  default  to
       KeyPress.  For example, <Control-comma> is equivalent to <Control-KeyPress-comma>.


       The  script  argument  to bind is a Tcl script, called the “binding script”, which will be
       executed whenever the given event sequence occurs.  Command will be executed in  the  same
       interpreter  that  the bind command was executed in, and it will run at global level (only
       global variables will be accessible).  If script  contains  any  %  characters,  then  the
       script  will  not  be  executed  directly.   Instead,  a  new  script will be generated by
       replacing each %, and the character following it, with information from the current event.
       The  replacement  depends  on the character following the %, as defined in the list below.
       Unless otherwise indicated, the replacement string is the decimal value of the given field
       from  the  current  event.   Some of the substitutions are only valid for certain types of
       events;  if they are used for other types of events the value substituted is undefined.

       %%   Replaced with a single percent.

       %#   The number of the last client request processed by the server (the serial field  from
            the event).  Valid for all event types.

       %a   The  above  field  from the event, formatted as a hexadecimal number.  Valid only for
            Configure events.  Indicates the  sibling  window  immediately  below  the  receiving
            window in the stacking order, or 0 if the receiving window is at the bottom.

       %b   The  number  of  the button that was pressed or released.  Valid only for ButtonPress
            and ButtonRelease events.

       %c   The count field from the event.  Valid only for Expose events.  Indicates that  there
            are count pending Expose events which have not yet been delivered to the window.

       %d   The  detail  or  user_data  field  from  the  event.   The %d is replaced by a string
            identifying the detail.  For Enter, Leave, FocusIn, and FocusOut events,  the  string
            will be one of the following:

                   NotifyAncestor          NotifyNonlinearVirtual
                   NotifyDetailNone        NotifyPointer
                   NotifyInferior          NotifyPointerRoot
                   NotifyNonlinear         NotifyVirtual

            For ConfigureRequest events, the string will be one of:

                   Above                   Opposite
                   Below                   None
                   BottomIf                TopIf

            For  virtual  events,  the  string  will be whatever value is stored in the user_data
            field when the event was created (typically with event generate), or the empty string
            if  the  field  is  NULL.   Virtual events corresponding to key sequence presses (see
            event add for details) set the user_data to NULL.  For events other than  these,  the
            substituted string is undefined.

       %f   The  focus  field from the event (0 or 1).  Valid only for Enter and Leave events.  1
            if the receiving window is the focus window or a descendant of the  focus  window,  0

       %h   The  height field from the event.  Valid for the Configure, ConfigureRequest, Create,
            ResizeRequest, and Expose events.  Indicates the  new  or  requested  height  of  the

       %i   The window field from the event, represented as a hexadecimal integer.  Valid for all
            event types.

       %k   The keycode field from the event.  Valid only for KeyPress and KeyRelease events.

       %m   The mode field from the event.   The  substituted  string  is  one  of  NotifyNormal,
            NotifyGrab,  NotifyUngrab,  or  NotifyWhileGrabbed.   Valid  only for Enter, FocusIn,
            FocusOut, and Leave events.

       %o   The override_redirect field from the  event.   Valid  only  for  Map,  Reparent,  and
            Configure events.

       %p   The  place  field  from  the  event,  substituted as one of the strings PlaceOnTop or
            PlaceOnBottom.  Valid only for Circulate and CirculateRequest events.

       %s   The state field from the event.  For  ButtonPress,  ButtonRelease,  Enter,  KeyPress,
            KeyRelease,  Leave,  and  Motion  events,  a  decimal  string  is  substituted.   For
            Visibility, one of the strings VisibilityUnobscured, VisibilityPartiallyObscured, and
            VisibilityFullyObscured is substituted.  For Property events, substituted with either
            the string NewValue (indicating that the property has been created  or  modified)  or
            Delete (indicating that the property has been removed).

       %t   The  time  field  from the event.  This is the X server timestamp (typically the time
            since the last server reset) in milliseconds, when the  event  occurred.   Valid  for
            most events.

       %w   The  width field from the event.  Indicates the new or requested width of the window.
            Valid only for Configure, ConfigureRequest, Create, ResizeRequest, and Expose events.

       %x, %y
            The x and y fields from the event.  For ButtonPress, ButtonRelease, Motion, KeyPress,
            KeyRelease,  and  MouseWheel  events,  %x  and  %y indicate the position of the mouse
            pointer relative to the receiving window.  For key events on the Macintosh these  are
            the  coordinates of the mouse at the moment when an X11 KeyEvent is sent to Tk, which
            could be slightly later than the time of the physical press or  release.   For  Enter
            and  Leave  events, the position where the mouse pointer crossed the window, relative
            to the receiving window.  For Configure and Create requests, the x and y  coordinates
            of the window relative to its parent window.

       %A   Substitutes  the UNICODE character corresponding to the event, or the empty string if
            the event does not correspond  to  a  UNICODE  character  (e.g.  the  shift  key  was
            pressed).  On  X11,  XmbLookupString  (or  XLookupString when input method support is
            turned off) does all the work of translating from the event to a  UNICODE  character.
            On  X11,  valid  only  for  KeyPress event. On Windows and macOS/aqua, valid only for
            KeyPress and KeyRelease events.

       %B   The border_width field from the event.  Valid only for  Configure,  ConfigureRequest,
            and Create events.

       %D   This  reports  the delta value of a MouseWheel event.  The delta value represents the
            rotation units the mouse wheel has been moved. The sign of the value  represents  the
            direction the mouse wheel was scrolled.

       %E   The  send_event  field  from the event.  Valid for all event types.  0 indicates that
            this is a “normal” event, 1 indicates that it is a  “synthetic”  event  generated  by

       %K   The  keysym  corresponding to the event, substituted as a textual string.  Valid only
            for KeyPress and KeyRelease events.

       %M   The number of script-based binding patterns matched so far for the event.  Valid  for
            all event types.

       %N   The  keysym  corresponding to the event, substituted as a decimal number.  Valid only
            for KeyPress and KeyRelease events.

       %P   The name of the property being updated or deleted (which may be converted to an XAtom
            using winfo atom.) Valid only for Property events.

       %R   The  root  window identifier from the event.  Valid only for events containing a root

       %S   The subwindow window identifier from the event, formatted as  a  hexadecimal  number.
            Valid only for events containing a subwindow field.

       %T   The type field from the event.  Valid for all event types.

       %W   The  path  name  of the window to which the event was reported (the window field from
            the event).  Valid for all event types.

       %X, %Y
            The x_root and  y_root fields from the event.  If a virtual-root  window  manager  is
            being  used  then  the  substituted  values are the corresponding x-coordinate and y-
            coordinate in the virtual root.  Valid only for  ButtonPress,  ButtonRelease,  Enter,
            KeyPress,  KeyRelease,  Leave  and  Motion events.  Same meaning as %x and %y, except
            relative to the (virtual) root window.

       The replacement string for a %-replacement is formatted as  a  proper  Tcl  list  element.
       This  means  that  spaces  or  special  characters  such  as  $  and  { may be preceded by
       backslashes.  This guarantees that the string will be passed through the Tcl  parser  when
       the  binding  script  is evaluated.  Most replacements are numbers or well-defined strings
       such as Above;  for these replacements no special formatting is ever necessary.  The  most
       common  case where reformatting occurs is for the %A substitution.  For example, if script
              insert %A
       and the character typed is an open square bracket, then the script actually executed  will
              insert \[
       This  will  cause  the  insert  to  receive  the  original replacement string (open square
       bracket) as its first argument.  If the extra backslash had not been added, Tcl would  not
       have been able to parse the script correctly.


       It  is  possible  for  several  bindings  to  match  a given X event.  If the bindings are
       associated with different tag's, then each of the bindings will be executed, in order.  By
       default,  a  binding for the widget will be executed first, followed by a class binding, a
       binding for its toplevel, and an all binding.  The bindtags command may be used to  change
       this  order  for  a  particular  window  or  to associate additional binding tags with the

       The continue and break commands may be  used  inside  a  binding  script  to  control  the
       processing of matching scripts.  If continue is invoked within a binding script, then this
       binding script, including all other “+”  appended  scripts,  is  terminated  but  Tk  will
       continue  processing binding scripts associated with other tag's.  If the break command is
       invoked within a binding script, then that script terminates and no other scripts will  be
       invoked for the event.

       Within  a  script  called from the binding script, return -code ok may be used to continue
       processing (including “+” appended scripts), or return -code break may  be  used  to  stop
       processing all other binding scripts.

       If  more  than one binding matches a particular event and they have the same tag, then the
       most specific binding is chosen and its script is  evaluated.   The  following  tests  are
       applied, in order, to determine which of several matching sequences is more specific:

              (a)    an  event  pattern  that specifies a specific button or key is more specific
                     than one that does not;

              (b)    a longer sequence (in terms of number of events matched)  is  more  specific
                     than a shorter sequence;

              (c)    if  the  modifiers specified in one pattern are a subset of the modifiers in
                     another pattern, then the pattern with more modifiers is more specific;

              (d)    a virtual event whose physical pattern matches the sequence is less specific
                     than the same physical pattern that is not associated with a virtual event;

              (e)    given a sequence that matches two or more virtual events, one of the virtual
                     events will be chosen, but the order is undefined.

       If the matching sequences contain more than one event, then tests (c)-(e) are  applied  in
       order  from  the  most  recent event to the least recent event in the sequences.  If these
       tests fail to determine a winner, then  the  most  recently  registered  sequence  is  the

       If  there  are  two (or more) virtual events that are both triggered by the same sequence,
       and both of those virtual events are bound to the same window tag, then only  one  of  the
       virtual events will be triggered, and it will be picked at random:
              event add <<Paste>> <Control-y>
              event add <<Paste>> <Button-2>
              event add <<Scroll>> <Button-2>
              bind Entry <<Paste>> {puts Paste}
              bind Entry <<Scroll>> {puts Scroll}
       If  the  user  types  Control-y,  the  <<Paste>>  binding will be invoked, but if the user
       presses button 2 then one of either the <<Paste>>  or  the  <<Scroll>>  bindings  will  be
       invoked, but exactly which one gets invoked is undefined.

       If  an X event does not match any of the existing bindings, then the event is ignored.  An
       unbound event is not considered to be an error.


       When a sequence specified in a bind command contains more than one event pattern, then its
       script  is  executed  whenever  the recent events (leading up to and including the current
       event) match the given sequence.  This means, for example, that if  button  1  is  clicked
       repeatedly the sequence <Double-ButtonPress-1> will match each button press but the first.
       If extraneous events that would prevent a match occur in the middle of an  event  sequence
       then  the  extraneous  events  are ignored unless they are KeyPress or ButtonPress events.
       For example, <Double-ButtonPress-1> will match a sequence of presses  of  button  1,  even
       though  there  will  be  ButtonRelease  events  (and  possibly  Motion events) between the
       ButtonPress events.  Furthermore, a KeyPress event may be preceded by any number of  other
       KeyPress  events  for  modifier  keys  without  the modifier keys preventing a match.  For
       example, the event sequence aB will match a press of the a key, a release of the a key,  a
       press  of  the Shift key, and a press of the b key:  the press of Shift is ignored because
       it is a modifier key.  Finally, if several Motion events occur in a row, only the last one
       is used for purposes of matching binding sequences.


       If  an  error  occurs  in executing the script for a binding then the bgerror mechanism is
       used to report the error.  The bgerror command will be executed at global  level  (outside
       the context of any Tcl procedure).


       Arrange  for  a string describing the motion of the mouse to be printed out when the mouse
       is double-clicked:
              bind . <Double-1> {
                  puts "hi from (%x,%y)"

       A little GUI that displays what the keysym name of the last key pressed is:
              set keysym "Press any key"
              pack [label .l -textvariable keysym -padx 2m -pady 1m]
              bind . <Key> {
                  set keysym "You pressed %K"


       bgerror(3tcl), bindtags(3tk), event(3tk), focus(3tk), grab(3tk), keysyms(3tk)


       binding, event