Determine which bindings apply to a window, and order of evaluation


(bindtags window ?tagList?)


When a binding is created with the bind procedure, it is associated either with a particular window such as .a.b.c, a class name such as Button, the constant "all", or any other string. All of these forms are called binding tags. Each window contains a list of binding tags that determine how events are processed for the window. When an event occurs in a window, it is applied to each of the window's tags in order: for each tag, the most specific binding that matches the given tag and event is executed. See the bind procedure for more information on the matching process.

By default, each window has four binding tags consisting of the name of the window, the window's class name, the name of the window's nearest toplevel ancestor, and "all", in that order. Toplevel windows have only three tags by default, since the toplevel name is the same as that of the window. The bindtags procedure allows the binding tags for a window to be read and modified.

If bindtags is invoked with only one argument, then the current set of binding tags for window is returned as a list. If the tagList argument is specified to bindtags, then it must be a proper list; the tags for window are changed to the elements of the list. The elements of tagList may be arbitrary strings; however, any tag starting with a dot is treated as the name of a window; if no window by that name exists at the time an event is processed, then the tag is ignored for that event. The order of the elements in tagList determines the order in which binding scripts are executed in response to events. For example, the call

(bindtags .b '("all" *root* "Button" .b))
reverses the order in which binding scripts will be evaluated for a button named .b so that "all" bindings are invoked first, following by bindings for .b's toplevel (*root* or ``.''), followed by class bindings, followed by bindings for .b. If tagList is an empty list then the binding tags for window are returned to the default state described above.

The bindtags procedure may be used to introduce arbitrary additional binding tags for a window, or to remove standard tags. For example,

(bindtags .b '(.b "TrickyButton" *root* "all"})
replaces the Button tag for .b with TrickyButton. This means that the default widget bindings for buttons, which are associated with the Button tag, will no longer apply to .b, but any bindings associated with TrickyButton (perhaps some new button behavior) will apply.



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