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| superclass: snip% | 
A button with a text label.
constructor
(new text-button-snip% [label label] [callback callback]) → (is-a?/c text-button-snip%) label : string? callback : ((is-a?/c text-button-snip%) (is-a?/c event%) . -> . void) 
The callback is called when the button is clicked.