On by default. Should be zero'd for doc ball builds.
web-ext = html midi pdf png txt ly signature
-footify = $(PYTHON) $(step-bindir)/add-html-footer.py --name $(PACKAGE_NAME) --version $(TOPLEVEL_VERSION)
+# For docball, issue `make web CONTENT_NEGOTIATION='
+CONTENT_NEGOTIATION = --content-negotiation
+footify = $(PYTHON) $(step-bindir)/add-html-footer.py --name $(PACKAGE_NAME) --version $(TOPLEVEL_VERSION) $(CONTENT_NEGOTIATION)
footifymail = MAILADDRESS='http://post.gmane.org/post.php?group=gmane.comp.gnu.lilypond.bugs'