Mapping historical sundials

Hello, I would like to proceed with a mapping of the historical sundials present in my area, I would like to know if there is a defined syntax for their mapping, thanks.



Taking a look to the TagInfo historic=sundial | Tags | OpenStreetMap Taginfo seems that the tag "historic=sundial is an unofficial tag, not so used… I don’t know if is so correct to use it…

The only ‘sundial’ I’ve ever mapped is a large fountain styled in the shape of one on a square appropriately named ‘Largo della Meridiana’. Not tagged as one but did put a note on it for later revisit, which is just now. Looking in the wiki it seems display=sundial is part of the tagging. There’s only 9 tagged TagInfo as of now with historic=sundial, historic=sundial | Tags | OpenStreetMap Taginfo but almost 3K tagged in a combo with display=sundial.