As of OpenGL 3.x, primitive restart was added where when enabled if a particular user defined index was encountered, then the primitive creation was restarted (the biggest use case being triangle strips). I would like to make augment it as follows:

Primitive Restart Index 2 is enabled/disabled GL_PRIMITIVE_RESTART_INDEX_SOME_NICE_NAME when passed to glEnable/glDisable.
When enabled, any one of the draw commands which transfers a set of generic attribute array elements to the GL the following will occur when index of the vertex is equal to the primitive restart index
  • will restart the primitive
  • the index following is NOT an index for an attribute. Rather it specifies the value gl_SomeGoodSoundingName used by any of the shading stages

The initial value of
gl_SomeGoodSoundingName is 0 at the start of each draw command. For instancing, the value if reset to zero at the start of each instance.

The idea behind this is that there are a number of cases where an attribute is used as an index into an array. Very often, that index does not change a great deal. With this extension, one does not need to occupy an entire attribute for that index.