/**
* {@inheritDoc}
*/
public function invert()
{
// we can't invert a text set if it has any 'values' (ie, non range intervals) in it
// check for these and throw a error if we have any
foreach ($this->intervals as $interval) {
if ($interval[0] === $interval[1] and $interval[0] !== null) {
throw new \RuntimeException("I'm sorry I can't invert the text set('{$this}') because it contains values.");
}
}
return parent::invert();
}
