How to clear a render target with multiple attachments?

Questions
1

Im looking into how to clear several attachments of a WebGLRenderTarget. ChatGPT says its possible but it gives an extremely low level example using the gl context.

const t = new WebGLRenderTarget(1,1,{count:2})

renderer.setRenderTarget(t)
renderer.setClearColor(color1)
// ?? 
renderer.setClearColor(color2)
// ??

Alternatively i could draw a full screen quad and tell it to write different things to different attachments. I am curious how much is this slower than clear()?