more explanation on tesselation control shader

Hi forum,

I am going the recent opengl redbook and i am having it difficult to understand as mentioned in book :

“The amount of tesselation is controlled by specifying two sets of values: the inner and outer tesselation levels. The outer-tesselation levels control how the perimeter of the domain is subdivided…”

I believe the understand the above statement as it matches the examples in the book . Now check the following:

"…Similarly, the inner-tesselation levels specify how the interior of the domain is sub-divided


gl_TessLevelInner[0] = 3.0;
gl_TessLevelInner[1] = 4.0;

Could anyone in the forum help me to understand the above snippet along the attached image ? Does it mean that gl_TessLevelInner[0] = 3.0; subdivide the region into 3 regions and which are these regions ?