Class doc says:

"""
DO NOT USE THIS CLASS

This class was introduced as a part of an early proposal during the JSR-206 standardization process. The proposal was eventually abandoned but this class accidentally remained in the source tree, and made its way into the final version.

This class does not participate in any JAXP 1.3 or JAXP 1.4 processing. It must not be used by users or JAXP implementations.
"""