Load and compile an XSLT document (specified by filename or string)
    for repeated use in transforming XML.

def load_xslt(filename=None, xsl=None):
    '''Load and compile an XSLT document (specified by filename or string)
    for repeated use in transforming XML.
    '''
    parser = _get_xmlparser()
    if filename is not None:
        xslt_doc = etree.parse(filename, parser=parser)
    if xsl is not None:
        xslt_doc = etree.fromstring(xsl, parser=parser)

    return etree.XSLT(xslt_doc)