Describe format of an object/user and object/user id

[YarrikV]

The docs note the restrictions on the relations:

From here

In OpenFGA, relations can only have alphanumeric characters, underscores and hyphens. We recommend using underscore (_) to separate words and removing prepositions. E.g.: "can create a document" can become "can_create_document" or "create_document" if you are into brevity.

It would be helpful if the same kind of restrictions would be clarified on the other elements, such as the object type and identifier.

For example, you cannot use a ':' or '#' in the identifier, but I figured this out by trial-and-error. What other restrictions/limitations are there?