Existing Wording: Users are encouraged to register their extensions in the second registry, though this is not required. All that is required is that the extension is published in a context that is available for users of the extension. So, for example, if a particular extension is only used within a single institution, the definition of the extension can be placed on the institution's intranet. However since, by their nature, resources tend to travel well, it's always better to use the HL7 or other publicly accessible extension registries.

Comment:

Making an extension available isn't synonymous with advertising it in a registry. A widely used extension can still be available if the definition is on it on a public facing web site. Systems who have recieved resouces using that extension know the url. And there is no need to advertise on the HL7 or another registry.

Summary:

Clarify publishing extension vs. advertising them