'Remove items from the start of the list, without touching the parent.'

def trim_start(self, n=1):

    if (n > len(self.data)):
        raise IndexError(("Size    of    trim    too    large;    can't    trim    %s    items    from    a    list    of    size    %s." % (n, len(self.data))))
    elif (n < 0):
        raise IndexError('Trim    size    must    be    >=    0.')
    del self.data[:n]
    del self.items[:n]
    if self.parent:
        self.parent_offset += n
