So, a new version based on further feedback (bold are changes to the previous versions). Unless there is opposition, I would try to edit it on the wiki later.
The tag highway=footway is used for mapping minor pathways which are used mainly or exclusively by pedestrians.
Usage
Footways tend to be constructed and either paved or with smooth surface (compacted, wood or similar). The elderly and small children and quite often also wheelchair users can use them with ease. They tend to be in urban settings, but not always. Access is primarily for pedestrians, which is often specified by street signs (or implied by local law).
— Paths kept mainly by the fact of people walking on them or paths that are only minimally constructed are usually tagged as highway=path. Their surface might be uneven (typically ground) and one might need to be physically fit and situationally aware to use them. They tend to be located outside of urban enviromnent. Hiking trails are a typical example and sac_scale=, trail_visibility=, surface=* and access=* are useful. However, in some countries like the UK or others, this distinction does not hold and highway=footway can be used for these too.
For ways used mainly or exclusively by cyclists, use instead highway=cycleway.
For ways used mainly or exclusively by horses, use instead highway=bridleway.
For ways used mainly or exclusively for motorcycles, use instead highway=path + motorcycle=yes or motorcycle=designated.
For ways closed to cars but open to motorcycles, cyclists, horses or other users without clear primary user, use highway=path with appropriate access tags.
For wider pedestrianised streets, typically, lined with shops or commercial buildings, use the tag highway=pedestrian.
Where a pathway is designated for pedestrians but is also allowed for bicycles, you can use highway=footway and bicycle=yes or highway=path, foot=designated and bicycles=yes.
Dirt roads for mostly agricultural, forestry, etc. uses should be tagged as highway=track.
For tagging sidewalks that span a road, see Sidewalks.
I m not saying this is realiably at all! I am just saying there is a tendency (that those tags that have surface notfilled in will behave like the ones that have is a guess – I might be wrong of course). In general when using maps, one needs to be aware of the local area since a lot of things will mean something different in Paris and at a town 50 km from Kathmandu even if they are mapped and rendered the same.