wenzelm [Sat, 01 Mar 2014 22:46:31 +0100] rev 55828
clarified language markup: added "delimited" property;
type Symbol_Pos.source preserves information about delimited outer tokens (e.g string, cartouche);
observe Completion.Language_Context only for delimited languages, which is important to complete keywords after undelimited inner tokens, e.g. "lemma A pro";