The original is at Learn Prolog Now!. http://lpn.swi-prolog.org is a proxy server that rewrites the pages on the fly to embed SWISH inline. When this was done we settled for this warning. The embedded version is a nice idea, but the HTML of the original makes it raher hard to properly identify source code and examples. Ideally the source should be annotated such that the proxy doesn’t have to guess what is what. Better might be to reformat the material in Spinx-Prolog for creating interactive Prolog books
OMG, No 
Although a bit dated, you find why not at SWI-Prolog future directions