ATTR_STD_UV_TANGENT and ATTR_STD_UV_TANGENT_SIGN?

Archive Cycles Development
1

Hi,

I understood that ATTR_STD_UV type attribute will have UV values for every triangle corner.
Ie, if we have N indices, then number triangles/faces are N / 3. The number or corners are N / 3 * 3. So, ithe attribute buffer’s size is N / 3 * 3 * size(float2)

What are ATTR_STD_UV_TANGENT and ATTR_STD_UV_TANGENT_SIGN?
How are they related to Vertices / Faces / UVs?
ATTR_STD_UV_TANGENT_SIGN and Bitangent are same?

Thanks in advance.