BCP47 to CLDR conversion

[Martin Hosken via CLDR-Users]

Dear All,

Would someone be willing to walk me through how en-US maps to en_US when converting from BCP47 to CLDR via the algorithm in 3.3.1?

My take is:

1. Canonicalize the language tag: en-US -> en (through likelySubtags minimising)
2. und->root: en -> en
3. languageAlias matching: no match: en -> en
4. territoryAlias matching: no match: en -> en

I'm probably misunderstanding step 1. (Is there a reference for step 1 and what that subalgorithm is?)

TIA,
Yours,
Martin