Should invisible imply intangible?

[Paul Michael Reilly]

Richard Stallman writes:
...
 > What would people think of making invisible imply intangible?  Is
 > there any practical use for text which is invisible but not
 > intangible?

Invisible but tangible appealed to me for handling Rmail ignorable
headers using inbox format.  On the one hand I wanted to make these
headers invisible to the User but on the other hand I want to
add/remove text behind the scenes, so to speak, to the headers to
handle attributes and labels.  I can imagine that cursor movement
might get kind of weird around invisible but tangible text.

There are three or four other ways to solve the problem, each with its
own set of tradeoffs.  Invisible implying intangible also makes for a
useful solution.

My gut feel is that having the three choices of invisible, intangible
and hidden (which is both invisible and intangible) is the best
solution.  I'd also want to have a variable for each case like
buffer-invisibility-spec, e.g. buffer-intangible-spec and
buffer-hidden-spec.

-pmr