espocrm-base/application/Espo/Resources/metadata/fields/link.json

{
   "params":[
      {
         "name":"required",
         "type":"bool",
         "default":false
      },
      {
         "name":"audited",
         "type":"bool"
      }
   ],
   "actualFields":[
      "id"
   ],
   "notActualFields":[
      "name"
   ],
   "filter": true,
   "notCreatable": true
}