Mnemonic ID rules:

Can be assigned by NER Librarian or LSO, only.

Must be unique.

Limited to 16 characters.

Use enough characters to make the mnemonic easily understood, e.g.,
   "bibl-asian-st" is better than "bas."

Use all lower-case letters

No spaces, ampersands or plus signs allowed.

Underscores, dashes and periods are allowed.