/usr/bin/GSMarkupBrowser is in librenaissance0-dev 0.9.0-4+b4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/GNUstep/Applications/GSMarkupBrowser.app/GSMarkupBrowser
/usr/bin/../lib/GNUstep/Applications/GSMarkupBrowser.app/GSMarkupBrowser