Well, it’s even beyond control of canvasdraw.h and canvasdraw…
The error messages on all (!) public wims servers are related to the HTTP request:
Request-URI Too Long
The requested URL’s length exceeds the capacity limit for this server.
Apache/2.4.54 (Debian) Server at wims.univ-cotedazur.fr Port 443
So any text string of this length sent to wims via http (direct exec or createxo) will produce an error…
joke