glsl - specify buffer, but no assigdment to frag


i’m curious what will happen if I assign a render buffer (using glDrawBuffers for instance) to buffer #3, and fail to assign any value in my shader program to gl_FragData[3] -
will the buffer be filled with garbage or zeros or undefined or what?

Thank you!

Undefined - filled with nothing.

Undefined means it’s filled with anything. Unchanged, random data or black are possible examples.