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This should now work in the just-released version 3.0.
Textastic 3.0 is now available on the App Store.
There is a problem with IIS WebDAV servers. This will be fixed in Textastic 3.0 which is currently in review at Apple.
There's already one at http://feedback.textasticapp.com/topic/34688-automatic-sync-with-dropbox/
This is in Textastic 3.0.
The new highlighter is now in Textastic 3.0 and supports TextMate syntax definitions and themes.
I've added a combined undo/redo button instead (segmented control) in Textastic 3.0.
You can add your own TextMate-compatible bundles and themes in Textastic 3.0.
Customer support service by UserEcho
This should now work correctly in the just-released version 3.0.