Child() is not working in match_expression of presets (although the documentation suggests that it should)

[goodidea]

According to the JOSM documentation for tagging presets (https://josm.openstreetmap.de/wiki/TaggingPresets), any (valid) search expression should be able to be used for match_expression. At least that's how I understand the text in the documentation:

match_expression="search expression"
additional criteria for matching primitives, specified in JOSM search syntax. (since r17662)

However, child() does not seem to be supported in a match_expression (although it works fine in a search expression in JOSM!)

Examples:

• A preset for a node with match_expression="child highway=*"(or match_expression="child (highway)") never matches in JOSM (or has a false result). No matter if the node is a connected with a highway way or not.
• A preset for a node with match_expression="-child highway=*"(or match_expression="-child (highway)") on the other hand always matches (or has a true result).

(I tried all possible syntax notations…)

Is this a bug, a missing feature, or just a documentation flaw (something like only a subset of the expressions possible for search expressions can be used in match_expression)? If the latter is true, the documentation for match_expression should be made clearer and specify exactly which type of search expression can and cannot be used.

But my main question is: would it be possible to allow child()? for match_expression as well? That would be great and very helpful.

In the latest Vespucci version, for example, this is supported for presets and is used in ​Simon Poole's "beautified-JOSM-preset" (which is suitable for JOSM and Vespucci) for traffic_sign nodes (nodes connected to a highway should have a direction=* tag with forward|backward, whereas separate nodes should have a compass direction as a value for direction=* – for this you need 2 different presets to clearly distinguish this and offer corresponding values ​​for direction, e.g. in a combo).

Currently these presets work very well in Vespucci, but not in JOSM (see also this GitHub issue: ​https://github.com/simonpoole/beautified-JOSM-preset/issues/477).

[skyper]

match_expression is rarely used in defaultpresets. In fact in almost five years since it was added it is used only in three cases. I guess the feature is not well tested and I would expect that this is a bug. If not the documentation needs to reflect this.

[goodidea]

Yes, I know that it's rarely used in JOSM's defaultpresets.

But as soon as you start creating custom presets for example (e.g. for certain tag combinations), match_expression becomes very important and useful to avoid multiple matches in JOSM. In my custom presets (which are based on Simon Poole's "beautified-JOSM-preset") I currently use it 138 times ...

And JOSM's default presets also lack a preset for general traffic_sign=* tags (or traffic_sign:forward=*/traffic_sign:backward=*), where a match_expression with child() would be particularly useful. In the defaultpresets, there are only 2 presets for traffic_sign=city_limit and traffic_sign=maxspeed (a very limited selection), where a distinction would actually be necessary because of the direction tag, too ...

Anyway, it would be nice if match_expression could be improved.