You can add custom syntax definitions to Textastic by using TextMate bundles. See
http://www.textasticapp.com/v5/manual/lessons/How_...

A quick search for "twig tmbundle" in Google brought up this TextMate bundle which should work:
https://github.com/Anomareh/PHP-Twig.tmbundle

You can find a list of hardware keyboard shortcuts at http://www.textasticapp.com/v5/manual/lessons/Whic...

I'm not aware of a shortcut to delete the current line.

I'll see what I can do.

Thanks for letting me know!

Thank you!

Hrmm... Textastic is a sandboxed app and uses the standard NSDocument mechanisms. The Open panel and iCloud are completely handled by the operating system. Because Textastic is sandboxed, it has no access whatsoever to the open panel.

So I think that's probably something that needs to be fixed in Default Folder X.

Does this problem also happen in other apps like Apple's TextEdit?

You can just drag the file icon from Textastic's window title bar onto the other editor's dock icon. This will open the file in the other app while it is still open in Textastic.