'Constructs the whole text again.'

def _build(self, sane, vals):

    if (vals is None):
        return sane[0]
    full = []
    for (x, y) in zip(sane, vals):
        full.append(str(x))
        full.append(str(y))
    full.append(str(sane[(-1)]))
    return ''.join(full)
