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The code looks good to me, and it worked as expected on my iPad in the dockpanel example for this PR. Are you still seeing issues on your end @martaszmit? If so, what hardware are you using to test?

Yes, I'm testing it on my laptop dell precision 7550 with touch screen in the dockpanel example.
Right now it works as in this movie ( not sure if you are now able to see it):

If it works fine for you when would be possible to merge it deliver new version of Lumino? Maybe after update in my project, it will work as expected.

It could be that it is inconsistently generating the pointer events on your hardware. A way to check that would be to add a console log in handleEvent for the event type and watch what events are fired as you interact with the split handles.

Ok, I will check it today.
Is it ready to merge? If so, when can it be merged?

Once we think this is ready, I can merge and release on the same day. I'm happy to merge as-is since it is already an improvement, and then you can follow up based on more testing on your hardware.

I think would be great if it will be merged now, and I will test it, and go back to you if I will still have an issue with it, ok?

Sounds good, releasing now.

Congrats on your first merged pull request in this project! 🎉

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Done! https://github.com/jupyterlab/lumino/releases/tag/v2021.10.25

Thank you!
I'm coming back with some analysis. I already tested dockpanel example, and my app.
I can confirm that dockpanel example (https://lumino.readthedocs.io/en/latest/examples/dockpanel/index.html) works fine on my iPad, but it still doesn't work on my Dell laptop and doesn't work using browser developer tools ( on my and 4 more different laptops too).
In my app resizing doesn't work on my Dell Laptop and on my iPad either (probably some issue in my code, maybe some additional requirements should be full-fielded? Anyhow drag and drop widget works perfect).

It could be the combination of browser/OS on the Dell that is causing inconsistent pointerEvent emissions. As for your app, are you using the SplitPanel directly (as opposed to a subclass that adds other logic)? It could also be that something else in your app is catching events in the "capture" phase and they aren't getting to the SplitPanel handle nodes.

Thank you for hints, I already found an oversight in my app :) Now works fine on iPad, but still doesn't work on my laptop. I tested my app and dockpanel example on few laptops and browsers using developer tools (because only my laptop has a touch screen). Could you also test dockpanel example using developer tools on your computer, please? I wonder if it will work fine for you.

Interesting! I saw the same thing when I opened Developer Tools for my iPad. The drag-n-drop mostly works, but the events are sporadic (it selects the input box within the panel), and the split panel handles do not work. When I closed the Developer Tools, it returned to normal behavior. Mind opening a new issue to track this?

I opened a bug ticket for this issue (#254).
Maybe some could take a look on it, I'm not sure if I will be able to do so.

Thanks again @martaszmit!