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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def format_diff_xml(a_xml, b_xml):
 """Create a diff between two XML documents. Args: a_xml: str b_xml: str Returns: str : `Differ`-style delta """

    return '\n'.join(
        difflib.ndiff(
            reformat_to_pretty_xml(a_xml).splitlines(),
            reformat_to_pretty_xml(b_xml).splitlines(),
        )
    )