uniform keyword in HLSL

Question

it seems that in HLSL i can but dont have to provide the uniform keyword for variables which come from the application. right?

why is that so?

Answer 1

In HLSL global variables are considered uniform by default.

It's also settled that a variable coming out of the vertex shader stage for example is varying (HLSL doesn't need this keyword at all!).

Note that GLSL keywords uniform/varying are inherited from RSL (RenderMan shading language).