def serialize_all(nodes, stream=None, Dumper=Dumper,
        canonical=None, indent=None, width=None,
        allow_unicode=None, line_break=None,
        encoding=None, explicit_start=None, explicit_end=None,
        version=None, tags=None):
    """
    Serialize a sequence of representation trees into a YAML stream.
    If stream is None, return the produced string instead.
    """
    getvalue = None
    if stream is None:
        if encoding is None:
            stream = io.StringIO()
        else:
            stream = io.BytesIO()
        getvalue = stream.getvalue
    dumper = Dumper(stream, canonical=canonical, indent=indent, width=width,
            allow_unicode=allow_unicode, line_break=line_break,
            encoding=encoding, version=version, tags=tags,
            explicit_start=explicit_start, explicit_end=explicit_end)
    try:
        dumper.open()
        for node in nodes:
            dumper.serialize(node)
        dumper.close()
    finally:
        dumper.dispose()
    if getvalue:
        return getvalue()