I'm writing a custom MIB file and was wondering which characters I can use in textual object identifiers (OIDs), ie. in the strings that make up identifiers like iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifIndex.
It looks like only alphanumeric characters and hyphens are allowed. Also, two consecutive hyphens are forbidden as well (because they start a comment in a MIB file). But what are the exact rules, and where is that stated in the standard(s)?
The RFC documents for SMI contain clear descriptions on such entities, like
For the purposes of this specification, an ASN.1 module name begins with an upper-case letter and continues with zero or more letters, digits, or hyphens, except that a hyphen can not be the last character, nor can there be two consecutive hyphens.