You should not take wiki as iron rules. This is one of the more unclear tags. If you do take it strictly, it only includes " green space" and "pitches, nets ". It is mostly associated with entire grass fields, often containing multiple courts. The cover photo is simply a `=playground` that can be enclosed in it casually, if not excluded.
They have different surfaces. 5k `=recreation_ground` has `surface=` to differentiate.

And you should read osm.wiki/One_feature,_one_OSM_element#Situations_where_multiple_elements_may_be_needed concerning `natural=water` areas enclosing `waterway=` , as well as `area:highway=` for `highway=` lines.

Areas also don't explicitly show how the full 400m loop overlaps with the 100m starting line tail.

The `=recreation_ground` is used for the entire greass field. `=pitch` has been used for the exact soccer playing area excluding the border.

Please read discussion on `aeroway=runway` and `=swimming_pool`. `lanes=` only make sense on a line. They show directions explicitly.

Please don't upload personal edits or test on a live public database. This constitutes (accidental) vandalism. You should have upload comments to let others can help if you have mistakenly done something.

1. Please don't change the entire area. Add a new point separately.
2. Relevant upload comments please/

Please don't upload duplicate features. If you want to draw sidewalks, they should be drawn alongside at the exact location, not attached on the road.

Please don't upload vandalism.

Please don't remove the English from `name=`. Spaced bilingualism is the standard in Hong Kong.

This already has `=motor_vehicle=yes`

The criteria of between junction is because `highway=` is a functional classification. Therefore junctions determine changes in function. Legal and official classification are sufficient but not necessary conditions. They are not the sole criteria, only a correlation.

`highway=` classification is determined between junctions. So it can't directly change to another class in the middle.
And again, what is a "main line" can be argued. I can say Shun Long Rd is a very large interchange. Or you can see how long is Yuen Shin Rd, or Tsing Sha Hwy on Tsing Yi. Ma On Shan Rd and Tsing Yi North Coastal Rd may be claimed as entrance / exits as well.
Therefore to avoid such debate, `=motorway_link` is exceptionally used to indicate special problems.

1. This is already the case with Tunnel Area. They are not Expressway, but are using `=motorway`. I have suggested to change them to `=trunk` + `motorroad=yes`. For the issue at hand, `=motorway` is a special class that's not defined by function alone. However, it still needs to follow the convention of classification between junctions. It should not suddenly change in the middle, simply because of the Expressway Area limit
2. Airport Rd only leads to North Lantau Hwy. That's why `=motorway_link` was used as a stop-gap. To indicate it is connected to a `=motorway` only.
3. Tung Wing Rd is a Tunnel Area. Discovery Bay Tunnel is more exceptional, because it is a single carriageway, with no physically raised separation. It also depends on the definition of `=*_link`. Eg some people find Penny Bay's Highway is only an entrance/exit now, so it has been `=motorway_link`.

That's why `=motorway_link` has been used as a stop-gap despite its issues. That was a tentative solution for many problems.
Other debates:
Ma On Shan Road
Tsing Yi North Coastal Road
Tsing Tin Road
Hung Tin Road

`=motorway_link` is to be used where it leads to `=motorway`

Otherwise by this logic, `=motorway_link` has to be changed mid-way. This has been raised and opposed explicitly in some public discussions.

I already indicated this by `motorway=no`. In OSM, `=motorway` and `=motorway_link` are used between junctions, not the exact location.

3. Tung Wing Road is Tunnel Area. Therefore under existing guidelines, it is `=motorway`. However, this was not followed in Discovery Bay Tunnel.

1. In this case, it is because the sections of Airport Rd concerned is only connected to Expressway due to partial interchanges.

Hi please see previous discussions on the subject.
1. This is not in Expressway Area. Together with Tunnel Area, the usage of `=motorway`, `=trunk`, and `=primary` is debated. As a stop-gap, `=motorway_link` has been applied to them.
2. Route 8 ends east of the bridge. It doesn't include the sea channel crossing.