How is IN.worldRefl calculated?

I want to know how the world reflection vector in shaders is calculated so that I can manipulate it, but there is no documentation on what it does or how Unity calculates it. How is the reflection vector calculated and exactly what does it do?

WorldReflectionVector(data,normal)
reflect (data.worldRefl, half3(dot(data.internalSurfaceTtoW0,normal), dot(data.internalSurfaceTtoW1,normal), dot(data.internalSurfaceTtoW2,normal)))

That’s a part that can be found in compiled shader code if you add #pragma debug