code: function(ctx, term)
  {
     var rval = null;
     if(term in ctx)
     {
        if(ctx[term].constructor === String)
        {
           rval = ctx[term];
        }
        else if(ctx[term].constructor === Object && '@id' in ctx[term])
        {
           rval = ctx[term]['@id'];
        }
     }
     return rval;
  }
docs: Gets the iri associated with a term.
  
  @param ctx the context.
  @param term the term.
  
  @return the iri or NULL.