Comment 3 for bug 190247

I have no idea, I thought of supporting to revert the status of how it used to be. Perhaps James or Martin Pitt (uploader of that change) can give a better explanation.
Or we should file this to the Debian maintainer upstream?

This is the changelog note from 5.2-2ubuntu2:
  * Merge from debian unstable, remaining changes:
    - libbcel-java-doc: Add alternative dependency on libgcj-doc.
    - debian/control: Drop libbcel-java-doc's dependency to
      libxerces2-java-doc to a suggestion, since that is in multiverse.

This is how it was before (5.2-2ubuntu1) in Ubuntu debian/control:
Package: libbcel-java-doc
Architecture: all
Section: doc
Depends: libgcj-doc | classpath-doc, libxerces2-java-doc
Suggests: libbcel-java
Description: Documentation for Byte Code Engineering Library (BCEL)
 Documentation for the BCEL Java library which is used to manipulate Java
 bytecode.
 .
  Homepage: http://jakarta.apache.org/bcel/

This is the Debian debian/control (5.2-3):
Package: libbcel-java-doc
Architecture: all
Section: doc
Depends: classpath-doc, libxerces2-java-doc
Suggests: libbcel-java
Description: Documentation for Byte Code Engineering Library (BCEL)
 Documentation for the BCEL Java library which is used to manipulate Java
 bytecode.
 .
  Homepage: http://jakarta.apache.org/bcel/

I've added a new patch to set as Depends only "libxerces2-java-doc".