iOS: Screen reader accessibility: `highlightActiveLine` extension breaks navigate-by-line

[personalizedrefrigerator]

Describe the issue

When navigating using the "Lines" mode from the VoiceOver rotor in an editor with basicSetup, the cursor gets stuck on blank lines:

ScreenRecording_04-29-2025.12-41-35_1.mp4

Comparison: <textarea>: Navigation is able to continue past blank lines:

ScreenRecording_04-29-2025.12-48-16_1.mp4

Comparison: <div contenteditable="true">: Navigation is able to continue past blank lines (lines containing only a <br>):

ScreenRecording_04-29-2025.12-44-04_1.mp4

Update: I can't reproduce the issue in the "minimal editor" example — I suspect that the issue is related to basicSetup:

ScreenRecording_04-29-2025.12-51-44_1.mp4

Note: I can still reproduce the issue if I remove markdown() language support from the demo linked below.

Browser and platform

iOS 18.4.1/Safari

Reproduction link

https://codemirror.net/try/#c=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

[personalizedrefrigerator]

The issue seems to be related to the highlightActiveLine extension. If I copy basicSetup and remove highlightActiveLine, I can no longer reproduce the issue.

[marijnh]

The only thing the editor seems to be doing to the DOM in this situation is adding and removing those active line classes. That seems like the only reasonable way to implement a feature like active line highlighting, so I'm not really sure there's much that CodeMirror can do differently to work around this. As such, the navigation getting stuck here seems more like a VoiceOver issue.