Get an overlay thet fits the range [start, end).

def fit_overlays(self, text, start=None, end=None, **kw):
        """
        Get an overlay thet fits the range [start, end).
        """

        _text = text[start or 0:]
        if end:
            _text = _text[:end]

        m = self.regex.match(unicode(_text))

        if m:
            yield Overlay(text, (start + m.start(), start + m.end()),
                          props=self.props,
                          value=self.value(rxmatch=m))