Module Structure of ArcEdit.
===========================

The underlying RISC_OSLib structure is assumed here.

The low level stuff is h.txt and everything below it (txt, txt1, txt3,
txtar). Some other interfaces (txtwin, txtundo) provide extensions to the
txt interface.

h.txt is the main central abstraction of a text buffer.
c.txt1 is the main host-independent management of text buffers. h.txt1
  explains its data structures.
c.txtar is the main RISC OS-dependent implementation of graphics calls
  needed by txt1.
c.txt is just a trivial switch between txt1 and txtar.
txt3 manipulates multiple txtar windows, and is pretty small and simple.
txtundo provides the undo buffer which is attatched to each txt buffer.

Then there are various modules that provide services in terms of txt.

txtmisc is various facilities, e.g. tabbing.
txtfind is finding strings in a txt.
txtfile is loading/saving files to/from txts.
scrap provides a single central selection between several txts.
txtoptmenu provides a generic user interface to the display options provided
  by txtar.

Then there is the editor itself, which provdes the user interface:

txtedit is the main editor
message/shell/slist is the task window
editv is the version box
edit is startup, and icon bar handling.
