Hi Alex! Thank you - everything works swimmingly. I thought I had tried restarting Textastic, but perhaps I didn't do it with the correct folder structure. 

It's all working great. Thanks so much.

I see - here is my file: https://www.dropbox.com/s/h7o9zntgaridjf5/tcm-notes.sublime-syntax?dl=0

In case you're wondering, I'm a web developer who is now studying Traditional Chinese Medicine. I've been using my code editor to take notes, and have developed this syntax definition for rich note taking.

Thanks for the feedback, but I'm still having trouble enabling it.

So, the custom syntax I created is just a .sublime-syntax file, in YAML. I don't have a "Sublime Package folder"

In my Local files i've tried the following:

#Textastic/tcm.sublime-syntax

#Textastic/tcm/tcm.sublime-syntax

#Textastic/tcm/Syntaxes/tcm.sublime-syntax

None of these folder structures work to enable my custom syntax.