What is true of any created custom attribute or object class?

While it's best practice to put custom schema definitions in separate files, there's no technical restriction preventing them from being placed in existing schema files, though this is generally discouraged for manageability.

Only the OID branch needs to be registered (e.g., with IANA or a national body) for a company, not every individual custom attribute or object class name; the OID ensures uniqueness, not the name itself being globally registered.

Every custom attribute or object class defined within an LDAP schema must have a globally unique Object Identifier (OID). This OID ensures that the custom schema element is unambiguously identified and prevents naming collisions when integrating with other directories or schema definitions. OIDs are hierarchical and assigned to maintain uniqueness.

There is no restriction that custom attribute or object class names must not contain any numbers; they simply need to follow naming conventions.