formal notepad without any result;

added Syntax.default_root; simplified Syntax.parse operations; clarified treatment of syntax root for translation rules -- refrain from logical_type replacement; tuned error message;

eliminated obsolete Token.Malformed -- subsumed by Token.Error;

tuned @{datatype} using Syntax.pretty_priority (NB: postfix type application yields Syntax.max_pri, so arguments in prefix application require higher priority);