Expand description
Button widget.
+--------+
| frame |
+---+----+
| \----------\
+---+----+ +-----+-----+
| button | | (textbox) |
+--------+ +-----------+If a label string is provided, a Textbox label will be created as a
sibling to the Button element.
The push and release control functions target the frame node, and
assume that the first child is the button node.