[plt-scheme] Clean design of editor's Scheme parser, program nav. commands?

I've looked at a few editors -- Climacs, Hemlock, jove, GNU Emacs, Lispworks's
editor -- and now I'm starting to try out PLT Scheme.  My goal is to find a
clean set of commands for navigating through LISP/Scheme programs, or find
an incremental buffer parser and a set of navigation functions that I can
build my own commands on.

Were the PLT program-navigation commands copied from Emacs?  Are the under-
lying parsing and navigation functions all in color:text<%> and
scheme:sexp-snip<%>?  Can the editor get the parse tree, navigate through it,
and find an ending text location?

If anyone has done any work with PLT studying the completness of the design,
creating documentation for navigation commands that uses uniform terms
to describe the object parsed ("the non-symbolic form before point" or some-
thing even more specific) and the ending cursor location ("before the open
parenthesis of the list"), or creating use cases, I'd love to hear about it.

-- Derek