Changes for the registration of value prefixes

Hi all,

Currently we have an entry in the wiki page for the FragID Registration that says:

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Are those prefixes the same as the ones used in custom values like in subState or subType?

Technically no. They can be different and the prefixes used for custom values do not have to be registered. But it makes sense and
it is a recommended practice to be consistent and use the same prefix for both mechanisms in your custom data.

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Based on today's call discussion about encouraging developers to register their prefixes for attribute values, here is a proposal
for the new text:

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Technically no. However, it is strongly encouraged to A) be consistent and use the same prefix for both mechanisms in your custom
data and B) to register the prefixes even if they are only for attribute values. In such case it is recommended for the registered
URI to be a URL pointing to a public page where the attribute values are described.

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Thanks,
-yves