Address PR comments

specification/common/common.md

@@ -90,12 +90,14 @@ Names SHOULD follow these rules:
 - When a new namespace is necessary consider whether it should be a top-level
   namespace (e.g. `service`) or a nested namespace (e.g. `service.instance`).
 
-- Semantic conventions exist for 4 areas: for Resource, Span and Log attribute
-  and for Metric label keys. Identical namespaces or names in these areas MUST
-  have identical meanings. For example the `http.method` span attribute name
-  denotes exactly the same concept as the `http.method` metric label, has the
-  same data type and the same set of possible values (in both cases it records
-  the value of the HTTP protocol's request method as a string).
+- Semantic conventions exist for four areas: for Resource, Span and Log
+  attribute names as well as Metric label keys. In addition, for spans we have
+  two more areas: Event and Link attribute names. Identical namespaces or names
+  in all these areas MUST have identical meanings. For example the `http.method`
+  span attribute name denotes exactly the same concept as the `http.method`
+  metric label, has the same data type and the same set of possible values (in
+  both cases it records the value of the HTTP protocol's request method as a
+  string).
 
 - Semantic conventions MUST limit names to printable Basic Latin characters
   (more precisely to