Hello, there is only one version of Textastic for iOS available for purchase on the App Store at the moment: Textastic 6. This is a universal app that works on both iPad and iPhone.

Please have a look at the Purchased section on the App Store to redownload the app on your iPhone. See https://support.apple.com/en-us/HT201272 for details.

Hello, you can change the syntax definition in the File Properties popover without changing the file extension. The chosen syntax definition will from then on be used for all files with the same file extension.

Hello, you first need to navigate to the folder in the "Remote" section to which you want to upload the file before tapping on the Upload button.

I'm sorry, but per-file read-only mode is a very specific feature request that I think most users won't need.

Dropbox disabled their old API. I added support for the new Dropbox v2 API in Textastic 6.3.2 in April last year.

You are still using Textastic 5.3.1. 

Textastic 6 is the first paid upgrade since version 1.0 was released in 2010. 

Implementing split view multitasking, making the app universal and supporting iPad Pro required a rewrite of large parts of the app. Charging for Textastic 6 allows me to continue to dedicate resources to improving it.

Among other features, Textastic 6.1 added Google Drive remote connections. Textastic 6.2 added new fonts and the ability to open Git repositories from Working Copy as external folders. Emmet support and a JavaScript console was added in Textastic 6.3. Textastic 6.4 adds support for iOS 11.

You can purchase Textastic 6 on the App Store: https://itunes.apple.com/us/app/id1049254261?ct=support&at=11lNQP&pt=15967&mt=8

Hello,

the main editor currently does not support spell checking. The menu in your screenshot is a standard macOS menu. It is active when the cursor is in a text field (for example in a search text field), but not when the editor is active.

You can add custom syntax definitions to Textastic by using TextMate bundles. See
http://www.textasticapp.com/v6/manual/lessons/How_can_I_add_my_own_syntax_definitions__themes_and_templates.html

A search for "netlogo tmbundle" in Google brought up this TextMate bundle which should work:

https://github.com/textmate/logo.tmbundle

I'm not familiar with Netlogo, so I'm not sure how well the Logo bundle works for you. After installing the bundle in Textastic, you should be able to select a "Logo" syntax definition after opening a file.

I'll look into it. In previous iOS versions this wasn't possible, but maybe something changed there.