In strings and buffers, the only control characters allowed are
those that exist in ASCII; but for keyboard input purposes, you can
turn any character into a control character with `C-'. The
character codes for these non-ASCII control characters include the
2**26 bit as well as the code for the corresponding non-control
character. Ordinary terminals have no way of generating non-ASCII
control characters, but you can generate them straightforwardly
using X and other window systems.

Here's what I think is happening: The code that complains about
undefined characters handles uninsertable characters (things like ^=D7=91 a=
nd
meta-control-mouse-down) by translating them to visible representation.
So the message contains a real caret followed by =D7=91. That is, the first
character has no strong directionality, and the directionality is set by
the second character, a non-control =D7=91.

/Larry Denenberg
***@denenberg.com
http://larry.denenberg.com/