Associating textures with Unreal materials using USD

Where can I find some USD examples on how to use “unreal” render context to associate textures or parameters to an Unreal material. I already have this,

        def Shader "UnrealShader"
        {
            uniform token info:implementationSource = "sourceAsset"
            uniform asset info:unreal:sourceAsset = @/Game/MDL/Base/OmniGlass.OmniGlass@
            token outputs:out
        }

Now I want to add texture files to materials that accept texture files.