Class description
This attachment-ref references one or more of the color attachments to the system-framebuffer. Depending on the window system pixel format for the window, up to four attachments may be available:
If double buffering is available, there is a back-face, which holds the screen image as it is drawn, and a front-face, which holds the current contents of the screen. The two buffers get swapped when a scene is completely drawn.
If stereoscopic rendering is available, there is a left-side and right-side, representing the left and right eye viewpoints of a 3D viewing apparatus.

To select a subset of these attachments, the system-attachment tuple type has two slots:
side selects either the left-side or right-side, or both if set to f.
face selects either the back-face or front-face, or both if set to f.

If stereo or double buffering are not available, then both sides or faces respectively will be equivalent. All attachments can be selected by setting both slots to f, both attachments of a side or face can be selected by setting a single slot, and a single attachment can be targeted by setting both slots.

See also
color-attachment, default-attachment, depth-attachment, stencil-attachment, attachment-ref, color-attachment-ref