code: func (i *InputField) SetAcceptanceFunc(handler func(textToCheck string, lastChar rune) bool) *InputField {
  	i.accept = handler
  	return i
  }
docs: // SetAcceptanceFunc sets a handler which may reject the last character that was
  // entered (by returning false).
  //
  // This package defines a number of variables prefixed with InputField which may
  // be used for common input (e.g. numbers, maximum text length).