@openstreetmap/id-tagging-schema/data/fields/population/date.json

The OpenStreetMap tagging model used by the iD editor

{
    "key": "population:date",
    "type": "text",
    "label": "Population Date",
    "placeholder": "YYYY-MM-DD",
    "prerequisiteTag": {
        "key": "population"
    },
    "terms": [
        "census date"
    ]
}