Variant reordering

[Doug Ewell]

BCP 47, Section 4.1 ("Choice of Language Tag"), bullet point 6 has this 
to say about reordering variant subtags:

"If a variant lists a second variant in one of its 'Prefix' fields, the 
first variant SHOULD appear directly after the second variant in any 
language tag where both occur.  General purpose variants (those with no 
'Prefix' fields at all) SHOULD appear after any other variant subtags. 
Order any remaining variants by placing the most significant subtag 
first.  If none of the subtags is more significant or no relationship 
can be determined, alphabetize the subtags."

What does the word "significant" mean in this context?

I note that this section is not normative with regard to conformance or 
canonical form; it's something for humans to consider, not necessarily 
for software to enforce. But I'm curious.

--
Doug Ewell | Thornton, CO, USA
http://ewellic.org | @DougEwell ­