There is one open-source xerces-related file with missing copyright header

jaxp/src/java.xml/share/classes/com/sun/org/apache/xerces/internal/xinclude/XPointerSchema.java

I’m trying to trace the origin of this file and initially I thought that it’s a part of Apache Xerces but apparently no

There is no such file in Apache repo
http://svn.apache.org/viewvc/xerces/java/trunk/src/org/apache/xerces/xinclude/
and I didn’t find any revision that removes this file.

It seems like this file and other two files are OpenJDK-specific files and these files aren’t used

jaxp/src/java.xml/share/classes/com/sun/org/apache/xerces/internal/xinclude/XPointerSchema.java
jaxp/src/java.xml/share/classes/com/sun/org/apache/xerces/internal/xinclude/XPointerFramework.java
jaxp/src/java.xml/share/classes/com/sun/org/apache/xerces/internal/xinclude/XPointerElementHandler.java

My understanding is that initially support for XPointer was missing in Apache Xerces and Sun implemented support for XPointer. But now Apache Xerces supports XPointer and these files are no longer used.