'Noting column boundaries, look for the bottom-left corner of the cell.
It must line up with the starting point.'

def scan_left(self, top, left, bottom, right):

    colseps = {}
    line = self.block[bottom]
    for i in range((right - 1), left, (-1)):
        if (line[i] == '+'):
            colseps[i] = [bottom]
        elif (line[i] != '-'):
            return None
    if (line[left] != '+'):
        return None
    result = self.scan_up(top, left, bottom, right)
    if (result is not None):
        rowseps = result
        return (rowseps, colseps)
    return None
