def find_autosummary_in_files(filenames):
    """Find out what items are documented in source/*.rst.

    See `find_autosummary_in_lines`.
    """
    documented = []
    for filename in filenames:
        f = open(filename, 'r')
        lines = f.read().splitlines()
        documented.extend(find_autosummary_in_lines(lines, filename=filename))
        f.close()
    return documented