winalski@PSW.DEC.COM (Paul S. Winalski) (07/27/86)
Regarding David S. Bakin's questions concerning 0-length marked areas in TPU:
A marker in TPU can either be on a character or after the last character on
a line (the EOB point counts as a 0-length line for this purpose), but nowhere
else. Markers cannot be placed between characters, only on them. A couple
of results of this are:
1) It is not possible to place a marker on the top of the buffer. The closest
you can come is to mark the first character in the buffer. But then, if
you insert characters at the front of the buffer, it moves the marker
over. However, it *is* possible to put a marker on the end of the buffer.
2) You can only get 0-length ranges at the ends of lines (or at the end of
buffer point). Anywhere else, the range will contain at least one
character because markers are on characters rather than between them.
So you can have 0-length regions, but only in certain places. My personal
opinion is that, in retrospect, markers on characters instead of between them
was a design mistake. Unfortunately, it would be awfully difficult to
rectify it at this point--to change this fundamental behavior now would blow
away just about every section file in existence.
--PSW