Add a new title level to appease gendoc

specification/targets.yaml

@@ -42,7 +42,7 @@ groups:  # reusable blobs of files when prefixed with 'group:'
     - modules/event_context.rst
 
 
-title_styles: ["=", "-", "~", "+", "^", "`", "@"]
+title_styles: ["=", "-", "~", "+", "^", "`", "@", ":"]
 
 # The templating system doesn't know the right title style to use when generating
 # RST. These symbols are 'relative' to say "make a sub-title" (-1), "make a title