Older Api documentation I am currently using a older IntelHd Gpu which supports Opengl3.1 (Glsl #version140).  

While trying to locate the relevant Api for this version ,the Khronos site only provides  documentation for Opengl2.1 and Opengl4.5.    

On their Github page documentation for Opengl2.1 and Opengl4 is available.  

How to locate the Api for Opengl 3.1?
Older Opengl Api documentation can be found at this  Official Khronos Registry