CodeSet

JSON Schema provides the “enum” keyword to require a value from an array, which can be used to implement CodeSet validation.

"Authorisation1Code": {
 "description": "Specifies the level of approval ...",
 "enum":["AUTH","FDET","FSUM","ILEV"]
}

This can be enhanced to include documentation on what each value means,
using the oneOf/enum pattern:

"Authorisation1Code": {
 "description": "Specifies the level of approval ...",
 "enum":["AUTH","FDET","FSUM","ILEV"],
 "oneOf":[
  {"enum":["AUTH"], 
  "title":"PreAuthorisedFile", 
  "description":"Indicates a file has been pre authorised ..."}, 
  ... 
 ]
}

It’s also possible to include the titles as additional permitted values.
Beware that there are a few titles longer than 80 characters, hundreds longer than 40, and many with dashes, but none with sapces, in their name.

"Authorisation1Code": {
 "description": "Specifies the level of approval ...",
 "enum":["AUTH","PreAuthorisedFile","FDET", ... ],
 "oneOf":[
  {"enum":["AUTH","PreAuthorisedFile"], 
  "title":"PreAuthorisedFile", 
  "description":"Indicates a file has been pre authorised ..."}, 
  ... 
 ]
}