consider is_in:continent for automatic dropping or vaidator warning with autofix removal

[mkoniecz]

What steps will reproduce the problem?

1. Create node with is_in:continent=Eurasia
2. Run validator

What is the expected result?

Validator offers to remove it as unwanted or this tag is listed at ​https://wiki.openstreetmap.org/wiki/Discardable_tags

What happens instead?

Nothing

Please provide any additional information below. Attach a screenshot if possible.

Note that this tag is highly dubious, as both division Earth landmass into continents[1] and boundaries between continents[2] are mostly subjective and unverifiable.

OSM is not a place to map multiple unverifiable models of global-sized objects. And adding tens of thousands of is_in:continent to various objects is the worst way to do this.

This proposal (especially discardable tag part) appeared during discussing ​https://wiki.openstreetmap.org/wiki/Mechanical_Edits/Mateusz_Konieczny_-_bot_account/remove_is_in:continent_in_USA - see ​https://lists.openstreetmap.org/pipermail/talk-us/2019-March/019332.html

[1] ​https://en.wikipedia.org/wiki/File:Continental_models-Australia.gif
[2] ​https://en.wikipedia.org/wiki/Boundaries_between_the_continents_of_Earth

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2019-03-19 01:06:07 +0100 (Tue, 19 Mar 2019)
Build-Date:2019-03-19 02:30:51
Revision:14904
Relative:URL: ^/trunk

Identification: JOSM/1.5 (14904 en) Linux Ubuntu 16.04.6 LTS
Memory Usage: 427 MB / 869 MB (210 MB allocated, but free)
Java version: 1.8.0_201-b09, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: :0.0 1920x1080
Maximum Screen Size: 1920x1080
Dataset consistency test: No problems found

Plugins:
+ OpeningHoursEditor (34867)
+ buildings_tools (34904)
+ continuosDownload (82)
+ imagery_offset_db (34867)
+ measurement (34867)
+ reverter (34917)
+ todo (30306)

Validator rules:
+ ${HOME}/Desktop/tmp/unnecessary.validator.mapcss

Last errors/warnings:
- W: No configuration settings found.  Using hardcoded default values for all pools.
- W: Failed to add ${HOME}/Desktop/tmp/unnecessary.validator.mapcss to tag checker
- W: java.nio.file.NoSuchFileException: ${HOME}/Desktop/tmp/unnecessary.validator.mapcss