The Digit Size Options in registry.md say they use the following EBNF:

digit-size-option = "0" / (("1"-"9") [DIGIT])

This appears to accept 0, 1, 2, ..., 9, 10, 11, ..., 98, 99.

However, ECMA-402 restricts the range of some of these integers to be less. For example, minimum and maximum significant digits and minimum integer digits are restricted to the range 1-21:

https://tc39.es/ecma402/#sec-setnfdigitoptions