Numbering sequences: identifiers people can read — The format

A format is literal text plus tokens: {YYYY}, {YY}, {MM}, {DD}, and one run of {#…} whose length sets the zero-padding. WO-{YYYY}-{####} produces WO-2026-0042. Formats are validated when you SAVE the configuration, not when a record is created — an unknown token is a mistake you can fix while looking at it, rather than an error thrown from inside somebody's save six weeks later. The counter is the part worth understanding: it is never reused, so a deleted record leaves a gap rather than letting a number be issued twice.