In iOS WebKit Legacy the test fast/writing-mode/english-rl-text-with-spelling-marker.html fails to render any spelling dots. Moreover the spelling dots in the expected result LayoutyTests/fast/writing-mode/english-rl-text-with-spelling-marker-expected.html render truncated and with artifacts.
Created attachment 347551 [details] english-rl-text-with-spelling-marker-actual.png
Created attachment 347552 [details] english-rl-text-with-spelling-marker-expected.png
I ran the test in the iPhone X iOS Simulator using WebKit r234848.
The test passes in iOS WebKit2 following <http://trac.webkit.org/r235149> (bug #188800).
For some reason the test fails in iOS WebKit1 because we do not seem to tigger spell checking. I noticed that focusing the editable element and placing the insertion point at the end of the text then pressing the left arrow key and right arrow key makes us perform spell checking.