How can I show statement nbr and logical heirarchy as Visual Studio does?

MANASYS Jazz is a programming system that displays the user’s program in a RichTextBox, highlighting keywords and variables with various fonts and colors as it analyses the program and reacts to errors. Here’s an example

We are starting to encounter large programs, and so I’d like to enhance the editor to give statement numbers and indicate logic hierarchy, as Visual Studio does. With a larger program it would be useful to click [-] and have everything with PROCESS/END PROCESS, IF/END IF, etc collapsed, to be restored with [+]. But how is this done? I could easily prefix each line of text with a prefix area, but I haven’t found a font that contains the boxed + and -. Or does VS implement this with a different concept? Are there RichTextBox properties and methods that will help me?