def _getNodes(xml, XPath):
    """Retreive the 'value' attribute from a set of XML nodes.

    Parameters
    ----------
    xml : xml.etree.ElementTree.ElementTree
        XML data in the PXDataset.data attribute.

    XPath : str
        An XPath string used to the define the nodes of interest.

    Returns
    -------
    list of str
        A list containing the 'value' attribute for each node found

    """
    return [node.attrib["value"] for node in xml.getroot().findall(XPath)]