Lexicon schemas are capable of referencing schemas from other namespaces. MASL would sit in between an application-specific schema and the raw blob:
{
"$type": "example.calendar.event",
"title": "My awesome birthday party",
"preview": {
"$type": "ing.dasl.masl",
"src": {
"$link": "bafkrei…"
},
"description": "Me posing in front of a gazebo in the park",
"content-type": "image/jxl",
"content-length": 68608
}
}
Or, if the metadata properties are sufficient on their own, the MASL object could be the record itself (within the ing.dasl.masl collection).