Introduce `colonCombo` field type

[tordans]

There are tagging practices that extend the key with a number in order to simulate an array of values.

Similar solutions (Docs):

• The semiCombo uses semicolons to simulate the array:

   foo=bar;baz
  

• The multiCombo encodes the value (from a defined list of values) into the key:

  foo:bar=yes
  foo:baz=yes
  

In the case of the panoramax key, the semiCombo is limiting the number of images to about 6 due to each panoramax value and and the max length of the field. See openstreetmap/id-tagging-schema#1344 (comment)

The multiCombo is not used for this kind of tagging where the value is something unique.

Instead MapComplete adds numbers to the key:

panoramax=123,
panoramax:0=234
panoramax:1=345

Historically, there where other cases where this :1 key postfix was used but I am not sure if any still exist that are relevant for the tagging schema. Some where fallbacks from TIGER imports AFAIR and some where used for the deprecated parking schema.

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I am not sure if this one panoramax use case is worth adding another combo field type. But lets use this issue to find out…

[mnalis]

I am not sure if this one panoramax use case is worth adding another combo field type

Well, there are several other existing usages of key:0, key:1 etc.

For example several thousand uses of each of image:[0-9], url:[0-9], website:[0-9], and probably more than a few of less popular keys (alt_name:1, phone:1, and many others with few hundred uses or less)

The problem IMHO is that it does not seems very standardized in OSM which tags are eligible for such treatment -- theoretically, any tag might have that :0, :1 etc suffix added, but especially likely are the ones which have longer values (so much more likely to hit 255-char limit if ; as a separator were used). But most of it seems haphazard and poorly documented.

That being said, it would be useful especially on those more popular values (mostly containing URLs!)

[1ec5]

OpenHistoricalMap uses the subscripted syntax on source:#=* and image:#=*. For now, OpenHistoricalMap/iD#223 has hard-coded support into iD, but we would definitely appreciate support here in order to be able to define these subkeys as part of OHM’s tagging schema.

One wrinkle is that OHM starts the numbering at 1 (or maybe 2), not 0. The first source or image just uses the main key without a subscript.

[matkoniecz]

Personally, I am not convinced that this multiimage tagging is worth supporting or encouraging.

[tordans]

Personally, I am not convinced that this multiimage tagging is worth supporting or encouraging.

We should only add it to presets where it is established and the only feasible solution. And on the editor UI side make to not too obvious to not invite overuse.

But given those constraints... why would we not?

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An alternative to adding this as a preset field could be to just "enhance" the fields in iD to at least give visibility to existing tags.
Update: openstreetmap/iD#12005