def get_edus(rst_graph, namespace='rst'):
    """
    returns the elementary discourse units (EDUs) in the order they occur
    in the document.

    Parameters
    ----------
    rst_graph : RSTGraph
        a document graph representing an RS3 file
    namespace : str
        the namespace that contains the EDUs (default: 'rst')

    Returns
    -------
    edus : list of str
        a list of node IDs of RST segments (EDUs) in the order they occur
        in the RS3 file
    """
    return rst_graph.node[rst_graph.root]['metadata'][namespace+':edus']