While the spec is not clear about that (see https://github.com/w3c/pointerevents/issues/276) other implementations essentially limit "touch-action: none" to be preventing panning and zooming but not other built-in behaviour such as text selection or navigation.
<rdar://problem/47901131>
Created attachment 362375 [details] Patch
Created attachment 362376 [details] Patch
Committed r241760: <https://trac.webkit.org/changeset/241760>