Be clearer about error names table, but see issue 1219

Author: domenic

index.bs

@@ -5166,16 +5166,25 @@ The resulting behavior from creating and throwing an exception is language bindi
 exception entails in the ECMAScript language binding.
 
 
-<h4 id="idl-DOMException-error-names">{{DOMException}} error names</h4>
+<h4 id="idl-DOMException-error-names">Base {{DOMException}} error names</h4>
 
-The <dfn id="dfn-error-names-table" export>error names table</dfn> below lists all the allowed error names
-for {{DOMException}}, a description, and legacy code values.
+The <dfn id="dfn-error-names-table" export>error names table</dfn> below lists all the allowed error
+names for instances of the base {{DOMException}} interface, along with a description of what such
+error names mean, and legacy numeric error code values.
 
-<p class="warning">
-    The {{DOMException}} names marked as deprecated are kept for legacy purposes but their usage is discouraged.
-</p>
+<p class="note">Interfaces [=interface/inheriting=] from {{DOMException}}, in the manner described
+in [[#idl-DOMException-derived-interfaces]], will have their own names, not listed in this table.
+
+When [=exception/creating=] or [=exception/throwing=] a {{DOMException}}, specifications must use
+one of these names. If a specification author believes none of these names are a good fit for their
+case, they must
+<a href="https://github.com/heycam/webidl/issues/new?title=DOMException%20name%20proposal">file an issue</a>
+to discuss adding a new name to the shared namespace, so that the community can coordinate such
+efforts. Note that adding new use-case-specific names is only important if you believe web
+developers will discriminate multiple error conditions arising from a single API.
 
-Note: If an error name is not listed here, please file a bug as indicated at the top of this specification and it will be addressed shortly. Thanks!
+<p class="warning">The {{DOMException}} names marked as deprecated are kept for legacy purposes, but
+their usage is discouraged.
 
 Note: Don't confuse the "{{SyntaxError!!exception}}" {{DOMException}} defined here
 with ECMAScript's {{ECMAScript/SyntaxError}}.