put doc in a dir corresponding to the lang.
1) Subdirs are not supported.
2)a) href starting with ?? search the index.html#htoc number via pattern matching in xcas html help. (Qregexpr)
b)   href  starting with one ? or not ending with a   .html are sent to the search for keywords engine. 
3) href starting with ! will insert the link (typically a keyword) instead of trying to follow the link




