'Check attribution shape.
Return the index past the end of the attribution, and the indent.'

def check_attribution(self, indented, attribution_start):

    indent = None
    i = (attribution_start + 1)
    for i in range((attribution_start + 1), len(indented)):
        line = indented[i].rstrip()
        if (not line):
            break
        if (indent is None):
            indent = (len(line) - len(line.lstrip()))
        elif ((len(line) - len(line.lstrip())) != indent):
            return (None, None)
    else:
        i += 1
    return (i, (indent or 0))
