I am solving a electromagnetic numerical problem. I can construct the 3d Nedelec finite element with degree 1 (Edge03d) and the system matrix K. What I want to know is how the matrix K is been constructed in this case, especially how to assemble such global matrices.
I can find the paper discussing higher-order Nedelec element online, which is HIGH ORDER EDGE ELEMENTS ON SIMPLICIAL MESHES. Is there any good reference that FreeFEM++ implements for the Nedelec element of degree 1?

Thank you, Prof. Hecht. The information is very helpful. Is the sign of the term determined by the order of global node index, like sgn(global_index(j) - global_index(i))?