This shader is a wrapper for providing custom pixel and vertex shaders, while it is named screenspace_general there is nothing inherently screenspace only about this shader, it is merely the name that was chosen before it received extra functionality that allowed it to do more than just screenspace work, as such this is a general shader that can be used on brushes, decals, info_overlays, models, and more.

For more information about creating custom shaders, see the Custom Shaders reference page.