docs/devel/qapi-code-gen: Describe some doc markup pitfalls

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230427095346.1238913-1-armbru@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

docs/devel/qapi-code-gen.rst

@@ -1060,6 +1060,59 @@ For example::
    'returns': ['BlockStats'] }
 
 
+Markup pitfalls
+~~~~~~~~~~~~~~~
+
+A blank line is required between list items and paragraphs.  Without
+it, the list may not be recognized, resulting in garbled output.  Good
+example::
+
+ # An event's state is modified if:
+ #
+ # - its name matches the @name pattern, and
+ # - if @vcpu is given, the event has the "vcpu" property.
+
+Without the blank line this would be a single paragraph.
+
+Indentation matters.  Bad example::
+
+ # @none: None (no memory side cache in this proximity domain,
+ #              or cache associativity unknown)
+
+The description is parsed as a definition list with term "None (no
+memory side cache in this proximity domain," and definition "or cache
+associativity unknown)".
+
+Section tags are case-sensitive and end with a colon.  Good example::
+
+ # Since: 7.1
+
+Bad examples (all ordinary paragraphs)::
+
+ # since: 7.1
+
+ # Since 7.1
+
+ # Since : 7.1
+
+Likewise, member descriptions require a colon.  Good example::
+
+ # @interface-id: Interface ID
+
+Bad examples (all ordinary paragraphs)::
+
+ # @interface-id   Interface ID
+
+ # @interface-id : Interface ID
+
+Undocumented members are not flagged, yet.  Instead, the generated
+documentation describes them as "Not documented".  Think twice before
+adding more undocumented members.
+
+When you change documentation comments, please check the generated
+documentation comes out as intended!
+
+
 Client JSON Protocol introspection
 ==================================