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The radiobutton command creates a new window (given by the pathName argument) and makes it into a radiobutton widget. Additional options, described above, may be specified on the command line or in the option database to configure aspects of the radio button such as its colors, font, text, and initial relief. The radiobutton 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 radio button is a widget that displays a textual string or bitmap and a diamond called a selector. A radio button has all of the behavior of a simple button: it can display itself in either of three different ways, according to the state option; it can be made to appear raised, sunken, or flat; it can be made to flash; and it invokes a Tcl command whenever mouse button 1 is clicked over the check button.

In addition, radio buttons can be selected. If a radio button is selected then a special highlight appears in the selector and a Tcl variable associated with the radio button is set to a particular value. If the radio button is not selected then the selector is drawn in a different fashion. Typically, several radio buttons share a single variable and the value of the variable indicates which radio button is to be selected. When a radio button is selected it sets the value of the variable to indicate that fact; each radio button also monitors the value of the variable and automatically selects and deselects itself when the variable's value changes. By default the variable selectedButton is used; its contents give the name of the button that is selected, or the empty string if no button associated with that variable is selected. The name of the variable for a radio button, plus the variable to be stored into it, may be modified with options on the command line or in the option database. By default a radio button is configured to select itself on button clicks.

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