what's the point (re shift selection)

[Thomas Lord <lord@emf.net>]

What *is* "the point"?

In emacs, "the point" is the name of a potential
location for the gap.   Insert commands always
happen at the gap.  "the point" is the gap location
of interest.  It's "what we're talking about".   It's
a key element of the dynamic state.

That's all traditional.   That's done.  That's how
Emacs has always worked.

Ok, next new insight: what exactly do we mean by
"potential location for the gap"?

Trivially, the gap can be placed between any two
extant, adjacent characters.  That's again, traditional
Emacs behavior.

But there is a generalization..... specifically: drop
the the qualifier "adjacent" and say, instead:

The point represents the potential gap between
any two characters in the buffer.

So, sometimes the point is not "point-like" -- it
is a "fat cursor".   The point is a potential gap that
spans between two non-adjacent characters.

That is how shift selection behaves in other apps --
as if the point is clearly the name of an arbitrary
potential gap, not merely a potential gap between
two already adjacent characters.

The concept of a "tentative-mark" is to give a
direct expression to the idea of a "fat cursor" -- of
a point that actually spans many characters.

The phase sensitivity -- the "maybe-preserved-..."
and "preserved-..." variables -- that is, indeed, a kind
of "psychological" hack.   Those *are* ad hoc.  They
are hair, as hair goes.   But they are minimal hair. 
They default in all the right ways.  They are easy to
explain and deal with.    They are a feature that exists
at the intersection between "how people think with short
term memory" and "how the emacs command loop works".
They are TRT, imho.

Over and out.   I give up.   Back to work on my VM and,
now, thanks to (friendly, good) provocation by Stefan, also
back to work on Arch 2.0 if I can work up the courage to
squeeze it in.

Have fun.  Let's test this "meritocracy of ideas" concept
the hard way :-)

-t