'Create a fold-able region from a fold trigger block.
:param block: The block **must** be a fold trigger.
:type block: QTextBlock
:raise: `ValueError` if the text block is not a fold trigger.'

def __init__(self, block):

    if (not TextBlockHelper.is_fold_trigger(block)):
        raise ValueError('Not    a    fold    trigger')
    self._trigger = block
