If the callback object or function property is specified, it overrides (any or all) the default pergola.Key class methods. In this example the default keypress method is overridden by the specified pergola.Key.keypressPosInt, designed to filter positive integers. Learn more in the SVG magazine Keyboard Class article.
You can also specify min and max numeric thresholds, maxLength maximum string length number, baseValue string or number, initial value string or number, a target object and propName string property name on which to operate, and the associated fn callback function.
Full overflow management is implemented (with default or custom notifications).