You can now find detailed instructions on how to edit custom fonts in the manual at 

https://www.textasticapp.com/v9/manual/customization/custom_fonts.html

I could now confirm that the "Next App Window" keyboard shortcut is Cmd-` (backtick) on a US keyboard. 

Use "Globe-`" for "Split View" -> "Next Window".

If you hold the "globe" key on your external keyboard, iPadOS displays the available global shortcuts.

On my iPad it looks like this:

On my iPad, I can use the "Multitasking" -> "Next App Window" (Cmd-<) keyboard shortcut or the "Split View" -> "Next Window" (Globe-<) shortcut to switch the active split view app.

This is with a German keyboard. You probably have different keyboard shortcuts (probably Command-backtick) on a US keyboard. 

"To make the tab stay when you open another file, tap the file title or the pin button at the right side of the tab. The file is also kept open if you tap on the editor or open the same file by tapping on it a second time."

Good point, I'll add it to my todo list.

Ok, I see now how it breaks apart when there are many files with similar short file names and the same file extension. Thanks a lot for the screenshot!

I'll consider adding this as an option.

I'm glad you found a syntax definition that works for you.