This functionality is currently available only on Onshape's browser platform.
A Feature Studio is a tab containing FeatureScript, a programming language used to define your own custom features in Onshape.
FeatureScript is designed by Onshape for writing features, and more generally, working with 3D parametric models. The language is built into Onshape from the ground up, providing the foundation of Part Studio modeling and used to define Onshape standard features (like Extrude, Fillet and Shell).
For detailed information on how to use FeatureScript to create custom features, see Welcome to FeatureScript (opens in new tab).
For detailed information on using custom features within your Onshape account, see Custom Feature.
To customize the toolbar of Part Studios, Assemblies, or Feature Studios, see Document Toolbar and Document Menu.