Support new attribute tag description-docbook

`description-docbook` is the alternative tag to `description`, the
difference is that `description-docbook` expects docbook XML but not
plaintext.

Signed-off-by: Wen Liang <liangwen12year@gmail.com>

tools/generate-docs-nm-settings-docs-merge.py

@@ -111,6 +111,13 @@ def node_set_attr(dst_node, name, nodes):
         dst_node.set(name, x)
 
 
+def find_first_not_none(itr):
+    for i in itr:
+        if i is not None:
+            return i
+    return None
+
+
 ###############################################################################
 
 gl_only_from_first = False
@@ -173,6 +180,11 @@ for setting_name in iter_keys_of_dicts(settings_roots, key_fcn_setting_name):
         dbg("> > > > property_name: %s" % (property_name))
 
         properties_attrs = list([p.get(property_name) for p in properties])
+        description_docbook = find_first_not_none(
+            p_attr.find("description-docbook")
+            for p_attr in properties_attrs
+            if p_attr is not None
+        )
 
         if gl_only_from_first and properties_attrs[0] is None:
             dbg("> > > > skip (only-from-first")
@@ -193,5 +205,8 @@ for setting_name in iter_keys_of_dicts(settings_roots, key_fcn_setting_name):
         node_set_attr(property_node, "default", properties_attrs)
         node_set_attr(property_node, "description", properties_attrs)
         node_set_attr(property_node, "alias", properties_attrs)
+        if description_docbook is not None:
+            property_node.insert(0, description_docbook)
+
 
 ET.ElementTree(root_node).write(gl_output_xml_file)