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Well, the extension of spaces to tabs actually isn't done by Textastic but by the TextExpander snippet expansion.

So you can either disable TextExpander support in Textastic's settings (if you haven't installed TextExpander on your device) or you can deactivate this in the TextExpander app.
1. Connect your device to your computer and open iTunes.

2. Select your your device in iTunes. Select the Summary tab.

3. Click on the Serial Number black label. It doesn’t look like something you can click on, unfortunately, making this more of a “hidden feature”. Serial Number will turn into Identifier (UDID).

4. Unfortunately this is another non-intuitive step. After you see Identifier (UDID) displayed, copy it to your OS clipboard with Ctrl-C (Windows) or Command-C (Mac). And here’s the subtle trick…

Most people try to highlight the UDID - which is almost the universally recognized way to copy something - but for some reason Apple decided to make this unable to be selected. You can’t highlight it. Just hit Ctrl-C or Command-C on this screen and trust that it’s copied to your OS clipboard. Now open an email or a text editor and paste in the clipboard contents. You now have your iPhone device ID.
I implemented #2 for Textastic 2.0 because I could use the same interface as for the FTP client.

I plan to add a feature that saves information about the used connection when you upload or download a file:

Say, you downloaded a file from your Dropbox. Textastic then saves the remote path and the connection used for the download. This creates a "link" between the local and the remote file.

You can then upload the file or download a newer version of the file with just one or two taps!

The cool thing is, that this works for Dropbox AND FTP and any other type of remote connection I might add in the future.
Yes, when you have a file opened in Textaxtic, you can tap on the "action" button (right-most button in the toolbar) and use the "Open In..." command to open the document in other apps registered for this file type.
Thanks for the detailed information. I'm sorry that you had to go through the trouble of reinstalling the app.
Although I can't reproduce it, I've limited this setting to a maximum value of 1000 for the next version.
This is now implemented for the next version.
Which iOS version are you running? I can't reproduce it on 4.2.
Did you try to restart the device?
Have a look at http://feedback.textasticapp.com/feedback/7436-dropbox-support/ for a discussion of Dropbox support. Actually, I've already started the implementation (along with FTP support).

As for Flex MXML files, I'll add the extension to the list of XML extensions, as MXML is XML.

In the future, please create separate feedback entries for every issue.

Thanks for your feedback!