Since the latest ST3 release (build 3067), the first in a long time, I have been cautiously optimistic. Here’s hoping that Jon will be willing and able to resuscitate and sustain the development cycle.

From the Build 3067 release notes:

How does that work? The feature appears as yet undocumented. My syntax definitions are written in JSON and subsequently compiled to XML (.tmLanguage). Thanks in advance.

Add this to the top level element:

    <key>hidden</key>
    <true/>

This will prevent the .tmLanguage file from appearing in the list of selectable syntax definitions, but will still enable it to be included within other syntax definitions, and programmatically assigned to a view.

Excellent—a fantastic and eagerly awaited feature. Thanks.

I am using the latest build (3069) and I have noticed that using the new hidden element in the language file removes it from the select list in the bottom right of the editor; however, the syntax is still assignable through the command palette.