<ending> during dal segno / da capo

[infojunkie]

At https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/ending/, the @number documentation says (emphasis mine):

Indicates which times the ending is played, similar to the time-only attribute used by other elements. While this often represents the numeric values for what is under the ending line, it can also indicate whether an ending is played during a larger dal segno or da capo repeat. Single endings such as "1" or comma-separated multiple endings such as "1,2" may be used.

It's not clear:

• How to specify that an ending should or should not be played during a jump back, and
• Which ending(s) should be played by default during a jump back