@openstreetmap/id-tagging-schema/data/fields/fax.json

The OpenStreetMap tagging model used by the iD editor

{
    "key": "fax",
    "keys": [
        "fax",
        "contact:fax"
    ],
    "type": "tel",
    "label": "Fax",
    "placeholder": "+31 42 123 4567"
}