The button command creates a new window (given by the
pathName argument) and makes it into a button widget.
options, described above, may be specified on the command line
or in the option database
to configure aspects of the button such as its colors, font,
text, and initial relief. The button 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 button is a widget
that displays a textual string or bitmap.
It can display itself in either of three different ways, according
the state option;
it can be made to appear raised, sunken, or flat;
and it can be made to flash. When a user invokes the
button (by pressing mouse button 1 with the cursor over the
button), then the Tcl command specified in the :command
option is invoked.