How is sorting and indexing by enum field done in PostgreSQL?

Question

PostgreSQL

How will Postgres sort by an ENUM field? By text label or by internal numeric representation (enumsortorder) ?
Is it possible to make a selection on an ENUM-type field using just enumsortorder, that is, not WHERE type = 'Type 1', where Type 1 is the text label of the ENUM-type value, WHERE type = 1, where 1 is the enumsortorder for a specific label?
And accordingly to build Btree on the ENUM field?
Thank you.

Answer 1

1. By enumsortorder
2. Not directly, or own function/operator/join/...etc.
3. Can