He means that the equations in the TeXmacs buffer are not rendered by LaTeX and imported as images (as in Emacs), but by TeXmacs. You can edit each part of the

He means that the equations in the TeXmacs buffer are not rendered by LaTeX and imported as images (as in Emacs), but by TeXmacs. You can edit each part of the rendered equation in realtime, without having to write source code as in LaTeX, similar to MSWord, but with the typesetting quality of LaTeX and with the movement keys of Emacs.