A DESCRIPTION OF THE PROBLEM :
XmlElementRef.java

at line 59 - 62 :
 
 * <pre>
 * public void setTerm(JAXBElement<? extends Operator>);
 * public JAXBElement<? extends Operator> getTerm();
 * </pre>

"<? extends Operator>" is not a HTML4 tag.
Therefore , I think that :
(1)"<" and ">" => "&lt;" and "& gt;"
or
(2)<pre>..</pre> => {@code ..}



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
     public void setTerm(JAXBElement<? extends Operator>);
     public JAXBElement<? extends Operator> getTerm();

ACTUAL -
     public void setTerm(JAXBElement);
     public JAXBElement getTerm();


URL OF FAULTY DOCUMENTATION :
https://docs.oracle.com/javase/8/docs/api/javax/xml/bind/annotation/XmlElementRef.html