External-citable references for letters, invoices, filing labels, email
subjects, PDF filenames, bank-transfer Verwendungszweck.
Format: <area>[.<project>...][.<YYMMDD>][.<collision-tag>]
- Date suffix YYMMDD (compact, not ISO).
- Collision-tag (.a, .b, ...) only when same <path>[.<date>] repeats.
- No doc-type taxonomy in v0.1 — collision-tag covers the disambiguation
case at lower memorisation cost.
- Lookup case-insensitive; display in m's preferred camelCase.
- Rename stability via projax.items.aliases[].
