Doxygen 1.8.11 prints the following warning, so I did what was mentioned:
[exec] warning: Tag `XML_SCHEMA' at line 1831 of file `Doxyfile' has become obsolete.
[exec] To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
[exec] warning: Tag `XML_DTD' at line 1837 of file `Doxyfile' has become obsolete.
[exec] To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
diff --git a/src/site/doxy/Doxyfile.in b/src/site/doxy/Doxyfile.in
index 8f26948..02dc6e8 100644
--- a/src/site/doxy/Doxyfile.in
+++ b/src/site/doxy/Doxyfile.in
@@ -1824,18 +1824,6 @@
XML_OUTPUT = xml
-# The XML_SCHEMA tag can be used to specify a XML schema, which can be used by a
-# validating XML parser to check the syntax of the XML files.
-# This tag requires that the tag GENERATE_XML is set to YES.
-
-XML_SCHEMA =
-
-# The XML_DTD tag can be used to specify a XML DTD, which can be used by a
-# validating XML parser to check the syntax of the XML files.
-# This tag requires that the tag GENERATE_XML is set to YES.
-
-XML_DTD =
-
# If the XML_PROGRAMLISTING tag is set to YES doxygen will dump the program
# listings (including syntax highlighting and cross-referencing information) to
# the XML output. Note that enabling this will significantly increase the size
