'Raises exception if buffer is changes beyound proxy object.'

def validate_buffer(self):

    if self.is_buffer_changed_outside():
        raise RuntimeError(((('buffer    was    modified    using    vim.command    or    ' + 'vim.current.buffer;    that    changes    are    untrackable    and    leads    to    ') + 'errors    in    snippet    expansion;    use    special    variable    `snip.buffer`    for    buffer    modifications.\n\n') + 'See    :help    UltiSnips-buffer-proxy    for    more    info.'))
