Removes XML declaration line from file or string passed in.
    If file_or_xml is not a file or string, it is returned as is.

def strip_xml_declaration(file_or_xml):
    """
    Removes XML declaration line from file or string passed in.
    If file_or_xml is not a file or string, it is returned as is.
    """

    xml_content = _xml_content_to_string(file_or_xml)
    if not isinstance(xml_content, string_types):
        return xml_content

    # For Python 2 compliance: replacement string must not specify unicode u''
    return _XML_DECLARATION_REGEX.sub(r'', xml_content, 1)