string = text .size (0..64)

policy_id = string
asset_name = string ; utf-8

files_details = 
  {
    name : string,
    mediaType : string,
    src : string / [* string]
  }

metadata_details = 
  {
    name : string,
    image : string / [* string], 
    ? mediaType : string,
    ? description : string / [* string],
    ? files : [* files_details]
  }

label_metadata = { * policy_id => { * asset_name => metadata_details } }

metadata = { 721 : uint => label_metadata }