How exactly did you create the new file and where did you save it? Did you use the "Create External File" command while offline?

(I don't use OneDrive myself, but I heard a few times that the OneDrive file provider is not very reliable.)

I can only point you to the Sublime Text documentation on syntax definitions at https://www.sublimetext.com/docs/syntax.html 

Please note that Textastic only supports the features of Sublime Text 3.0 syntax definitions, not later ones.

Maybe you can find a TextMate 1 bundle or Sublime Text 3 package of a language that is similar to Batari Basic and modify it?

Hello,

how did you download the TextMate bundle from GitHub?

Please try the following:

• go to https://github.com/nitaigao/racket-tmbundle in Safari on your iPad
• tap the green "Code" button and select "Download ZIP"
• Unzip the file in the Files app
• Copy the folder "racket-tmbundle-master" to "On my iPad/Textastic/#Textastic/"
• In Textastic, rename the folder to "racket.tmbundle"
• Go to Textastic's Settings -> Other and tap "Reload Customizations"

Now "Racket" should be listed in File Properties -> Syntax Definition after opening a file.

Yes, you are right. Currently the drag interaction of a tab (which can be used to create a new window from the tab) interferes with the reorder gesture when using a mouse or trackpad. So this means that reordering tabs currently only works when using your finger to drag tabs.

I'll see what I can do to make it work. 

Textastic 9.8.7 now uses MultiMarkdown 6 and supports file transclusion: 

Use {{some_other_file.md}} in a Markdown file to include other Markdown files.

See https://fletcher.github.io/MultiMarkdown-6/syntax/transclusion.html for details.

Ah, I see. Yes, you can add your own templates and also modify the built-in ones.

The templates are strings in a .json file. You can put them into the folder "Local Files/#Textastic/Templates". 

The default HTML template .json file can be found at https://github.com/blach/Textastic-Customization/blob/master/Templates/html.json

You can modify the html.json file and put it into the folder "Local Files/#Textastic/Templates/". As long as you don't change the uuid field in the .json file, it will be used instead of the templates that are built into the app.

This is described at https://github.com/blach/Textastic-Customization/blob/master/README.md#modifying-existing-templates

Please also have a look at this topic in the manual to see how to add the special folder "#Textastic" in Local Files:

https://www.textasticapp.com/v9/manual/customization/custom_syntax_themes_templates.html#adding-custom-templates