  Many programming problems call for turning geometrical thoughts into code:
tables, hierarchical structures, nests of objects, trees, forests, graphs, and
so on. Linear text does not do justice to such thoughts. But, it has been the
dominant programming medium for the past and will remain so for the foreseeable
future.
  This paper proposes a novel mechanism for conveniently extending textual
programming languages with problem-specific visual syntax. It argues the
necessity of this language feature, demonstrates the feasibility with a robust
prototype, and sketches a design plan for adapting the idea to other languages.
