Validation misses tag combination `highway=footway` and `area=yes`

[SilentSpike100@…]

What steps will reproduce the problem?

1. Create a closed way
2. Add tags highway=footway and area=yes
3. Run validation and observe that it doesn't complain

What is the expected result?

Tag combination is not valid and breaks routing services:
​https://wiki.openstreetmap.org/wiki/Tag:area:highway%3Dfootway

Expected that validation flags this and suggests use of area:highway

What happens instead?

Area should be listed in validation results

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

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2018-05-31 00:51:20 +0200 (Thu, 31 May 2018)
Build-Date:2018-05-30 22:58:01
Revision:13878
Relative:URL: ^/trunk

Identification: JOSM/1.5 (13878 en_GB) Windows 10 64-Bit
OS Build number: Windows 10 Home 1803 (17134)
Memory Usage: 735 MB / 1820 MB (144 MB allocated, but free)
Java version: 1.8.0_171-b11, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: \Display0 1920x1080, \Display1 1920x1080
Maximum Screen Size: 1920x1080
Dataset consistency test: No problems found

Plugins:
+ gpsblam (34095)
+ imagery_offset_db (34209)
+ terracer (34109)
+ turnrestrictions (34129)

Last errors/warnings:
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: java.io.IOException: Attribution is not loaded yet
- W: Region [WMS_BLOCK_v2] Resetting cache
- W: Region [WMTS_BLOCK_v2] Resetting cache

[Don-vip]

Who wrote this authoritative statement? "Combination of highway=footway + area=yes is incorrect, because it causes routing services to break down.". Writing highway=footway + area=yes or area:highway=footway is semantically the same. Routing software should be smart enough to understand that.