OnChangeOnChange — attaches an event handler to a point change event.
OnChange (sym, fn)
symAny Gamma symbol.
fnA function or method call.
A list containing the sym and
fn.
This method is a wrapper for the on_change function. In addition to applying
that function, it adds this change to the class's
_ChangeFunctions list. For more information, please refer
to Section 5.3, “Handling Events”.