This will be added in the next update.

Textastic fully supports iCloud Drive: if you store files in "iCloud" instead of "Local Files", files will be automatically synced across your devices.

In the iCloud Drive app or in Finder on macOS, you will find these files in the "Textastic" subfolder of iCloud Drive.

You can also use "Open…" to invoke the iOS document picker and open files from other apps including iCloud Drive. The document picker also allows you to pick whole folders from apps like the Git client Working Copy: http://blach.io/2016/08/02/opening-git-repository-folders-in-textastic-6-2/

This will be fixed in the next update.

That's probably related to the switch from the old UIWebView to the more performant WKWebView.

Textastic currently does not support multiple windows or tabs in the web preview, so creating a new window from JavaScript does not work properly at the moment, sorry.