src/Pure/PIDE/command_span.scala
2016-08-04 ago support for context block structure in Sidekick;
2015-03-17 ago misc tuning and simplification;
2015-03-15 ago clarified span position;
2015-03-13 ago simplified Command.resolve_files in ML, using blobs_index from Scala;
2015-03-12 ago clarified command content;
2015-03-12 ago tuned -- more uniform ML vs. Scala;
2014-10-28 ago find command span in buffer;
2014-08-12 ago maintain Command_Range position as in ML;
2014-08-12 ago separate module Command_Span: mostly syntactic representation;