Class description
A color-attachment-ref value references a particular color attachment to a framebuffer object.
system-attachment references one or more of the color attachments to the system-framebuffer.
color-attachment references one of the indexed color attachments to a user-created framebuffer.
default-attachment references the back buffer of the system-framebuffer or the first color attachment of a user framebuffer.

User-created framebuffer objects require OpenGL 3.0 or one of the GL_ARB_framebuffer_object or GL_EXT_framebuffer_object extensions.

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