So I did already know that TeXmacs is not a LaTeX frontend (LaTeX being a set of TeX macros concerned with content organization, e.g. it's what gives you complex notions of things like "chapter" and "section" that you don't get from tex-core or tex-plain), but rather a WYSIWYG/M editor similar to LyX (LyX uses LaTeX under the hood).
But I thought it does use the TeX engine under the hood for typesetting? I figured it's a WYSIWYG frontend that maps some sort of internal representation to a TeX output and throws it at TeX in the end, with its own LaTeX-type ideas for higher organization?