Great. I shall do my best to keep up! Fewer versions, each with more change, works for me too. If you’re looking at flipping, there is a bug in flipping an arc by line.
You can see this live at: https://my-pattern.cloud/patternEditor/tests/test_operationFlipByLine.html
Clicking the eyeball icon toggles the visibility of the wallpaper which is a screen capture from Seamly2D.
I working transformation can be seen at https://github.com/MrDoo71/PatternEditor/blob/master/scripts/geometry.js:1006.
(Though as I write this I realise i) I should update my version of seamly2d, and ii) there is a better place to post bugs, and iii) my-pattern.cloud’s ssl has just expired )