simple variant

Dear All,

I notice that the IANA registry has the following record:

Type: variant
Subtag: simple
Description: Simplified form
Added: 2015-12-29

So, in theory, the simple variant may occur on any tag. Is this the intention? I realise that if there is a long list of tags that it can occur on, it may not be worth listing them all. But I'm wondering what the thinking is behind this variant. Perhaps just pointing me to the original application form may be enough.

TIA,
Martin