Mine

When a package is changed in Ubuntu, the Maintainer field (in debian/control) is changed to indicate the Ubuntu team responsible for the Ubuntu specific changes (often "Ubuntu MOTU Developers <ubuntu-motu@lists.ubuntu.com>" for universe packages).  In order to ensure appropriate credit for the packaging work, the original maintainer is preserved in a new field: XSBC-Original0Maintainer.  This is a user-defined field (X) which is included in the .dsc file for the source package (S), the .deb file for the binary package (B), and the .changes file (C).

When the Maintainer field is adjusted, the value of XSBC-Original=Maintainer should match exactly to the previous value of Maintainer.