UI issue: Text edit mode

[Lars Clausen <lars raeder dk>]

I'm strong considering splitting diagram editing into a "normal" mode
and a "text-edit" mode.  It will allow for more powerful text editing
down the road, use of more shortcuts in normal mode, avoidance of the
"Delete destroys the object" in text-edit mode and more.  While I have
no problem with how to exit text-edit mode (Esc or clicking elsewhere),
I have my doubts about what would be best for entering.  My ideas so far
are

1) Press "Enter" to start editing text.  Pro: Frees all other keys for
shortcuts.  Con: Non-obvious
2) Press any letter key to start editing.  Pro: Natural start of writing
for many people.  Con: Loses some shortcuts, can't start writing with
non-letters or composite keys.
3) Press any non-modified key to start editing. Pro: Fully transparent
for English-speaking people.  Con: Loses a few more shortcuts, can't
start writing with more complex input.
4) Press any part of a character to start editing. Pro: Transparent for
everyone.  Con: Loses a lot of shortcuts, including many alt and some
ctrl-shift ones.

I'm favoring 3 over 2, even though it'd rule out using '1' for zoom
100%.  I think 4 would be confusing and hard to code.  But is 1 too
non-intuitive?  Are there better ways?  What do other programs get away
with?

-Lars