org.w3c.dom.xpath has existed in JDK/JAXP API package as part of org.w3c.dom package. However, it has not been included in the specification. Part of the reason could be that JDK/JAXP defines a separate javax.xml.xpath API.
Regardless of the JAXP specification, org.w3c.dom.xpath has always been public. More importantly, it provides features such as the support for any type that is missing from javax.xml.xpath (refer to JDK-8054196). For this reason, and to allow users to continue using the API after modularization, I hereby propose to make org.w3c.dom.xpath a formal part of the standard API.