error[preamble-enum-type]: preamble header `type` has an unrecognized value
 --> input.md:8:6
  |
8 | type: Unknown
  |      ^^^^^^^^ must be one of: `Standards Track`, `Meta`, `Informational`
  |
error[preamble-req-category]: preamble header `category` is only allowed when `type` is `Standards Track`
 --> input.md:8:1
  |
8 | type: Unknown
  | ------------- info: unless equal to `Standards Track`
  |
 ::: input.md:9:1
  |
9 | category: Core
  | ^^^^^^^^^^^^^^ remove this
  |