Vertex attributes that override the primary mesh when the MeshRenderer uses lightmaps in the Realtime Global Illumination system.
This vertex stream is used exclusively for UVs for real-time lightmaps.
When Unity renders a MeshRenderer that uses real-time lightmaps, Unity streams the data in MeshRenderer.enlightenVertexStream to `TEXCOORD2` instead of the data in Mesh.uv3]. For more information, see Lightmap UVs.
This data is not serialized. Unity calculates the UVs for the Realtime Global Illumination system during the precompute stage.