Property (key) field should suggest existing properties while typing.

Tagify?

Open Food Facts uses Tagify library. Each field with a taxonomy has a simple HTML:
<input type="text" name="labels" id="labels" class="text tagify-me" value="" lang="en" data-autocomplete="https://world.openfoodfacts.org/cgi/suggest.pl?tagtype=labels&" />. The data-autocomplete opens the link
https://world.openfoodfacts.org/cgi/suggest.pl?tagtype=labels&term=Tes which returns a JSON array: ["Tesco Nurture","Alimentos Artesanos de Navarra","PDO Montes de Granada","PDO Montes de Toledo","PGI Garbanzo de Fuentesaúco","Sulfites and SO2 > 10ppm","With natural sulfites","With sulfites","Without sulfites"]

Folksonomy Engine current API

The list of keys is here: https://api.folksonomy.openfoodfacts.org/keys and returns:

[

    {
        "k": "test",
        "count": 2,
        "values": 2
    },
    {
        "k": "photo_front",
        "count": 1,
        "values": 1
    }
]