Use 'in' or 'out' in layout when create tessellation evaluation shaders?

Question

In OpenGL Programming Guide, some code use 'in' in tessellation evaluation shader like this:

layout(triangles,equal_spacing,ccw,points) out;

and some times like this:

layout (quads,equal_spacing,cw) in;

the name of variables changes,some times it's out,some times in,I'm confused.And I changed it in my code, there are no differences,so what are the differences between in and out?

Answer 1

[...] the name of variables changes, some times it's out, some times in.

No it is not.

The Tessellation Evaluation Shader allows you to specify input layout qualifiers for the primitive-mode, vertex-spacing, and order.
The Tessellation Control Shader allows you to specify the output layout qualifier for the number of vertices.

See OpenGL Shading Language 4.60 Specification (HTML) - 4.4. Layout Qualifiers

The layout qualifier:

layout(triangles,equal_spacing,ccw,points) out;

is incorrect and causes a compile time error.