refined Markup_Tree implementation: stacked markup within each entry; tuned;
refined Markup_Tree implementation: stacked markup within each entry;
tuned;

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle