`preamble-date-...`

The ... header is a date.

Examples

error[preamble-date-last-call-deadline]: preamble header `last-call-deadline` is not a date in the `YYYY-MM-DD` format
 --> input.md:8:20
  |
8 | last-call-deadline: 2020/01/01
  |                    ^^^^^^^^^^^ input contains invalid characters
  |

error[preamble-date-created]: preamble header `created` is not a date in the `YYYY-MM-DD` format
  --> input.md:10:9
   |
10 | created: 2020/01/01
   |         ^^^^^^^^^^^ input contains invalid characters
   |

Explanation

The preamble-date-... family of lints make sure that dates in the front matter (or preamble) follow the correct format (YYYY-MM-DD.)