What is the syntax for a JSON:API Accept HTTP header with multiple extensions? I can't find it in the spec.

Here are some possibilities for a client that wants to use both the https://my-ext1 and https://my-ext2 extensions:

1. Accept: application/vnd.api+json; ext="https://my-ext1 https://my-ext2"
2. Accept: application/vnd.api+json; ext="https://my-ext1, https://my-ext2"
3. Accept: application/vnd.api+json; ext="https://my-ext1; https://my-ext2"
4. Accept: application/vnd.api+json; ext="https://my-ext1"; "https://my-ext2"
5. Accept: application/vnd.api+json; ext="https://my-ext1"; ext="https://my-ext2"