The identity arrow, which plays the role of return in arrow notation.
Transfers accumulation buffer values to the color buffer or buffers currently selected for writing. Each R, G, B, and A component is multiplied by the value given to accum, then multiplied by 2^n-1, clamped to the range [0, 2^n-1], and stored in the corresponding display buffer cell. The only fragment operations that are applied to this transfer are pixel ownership, scissor, dithering, and color writemasks.
wrap non-options into options
Return from mainLoop when any window is closed.