Has anyone used the embedding aspect of ECL significantly? I've used ECL as a standalone Lisp system, and also done fairly trivial embedding where there isn't m

Has anyone used the embedding aspect of ECL significantly? I've used ECL as a standalone Lisp system, and also done fairly trivial embedding where there isn't much more interaction than there would be if you communicated with an external Lisp system via a pipe. But curious how usable the API on the C side is for interacting with an embedded ECL, to call functions and pass data across the boundary in either direction (cl_object, cl_def_c_function, etc.). The documentation for that part seems pretty sparse.