What feature is at play when Ctrl+Shift+Alt+U,E "types" an unprintable hex 000E?

Ctrl-Shift-U is the short-cut to start entering a full unicode character by hand. For example, here I've typed: Ctrl-Shift-U 0 0 b 0 enter to get the degree symbol: ° which is unicode 00b0. Here is 2665, the heart: ♥

For a list of unicode symbols start here: http://en.wikipedia.org/wiki/Unicode

The glyph unicode u+240E ␎ is used when referring to u+000E aka SO (Shift Out) or ctrl-N, basically any control code is rendered as a symbol by adding 2400_hex to the control code to get the equivalent unicode glyph. (aside: The wrong glyph appears in Ubuntu 12.04. It should be SO not SS. see below)

To see the different glyphs available use either the character map icon utility or one of the following terminal commands:

gnome-character-map
gucharmap

Consequent to this, by holding down the right button and "mousing" over the map the unicode in the bottom corner and the symbol with its defining font (if any) are displayed (circled in green for this example). In this case, for U+000E, the "character" is not printable so there is no symbol and thus no font. The other squares, highlighted in yellow for this example, are similarly unprintable because they are also control codes and associated with the characters circled in yellow. Thus ctrl-D or ^D is the same as U+0004.

To see this, open a new terminal window and instead of using the standard ^D convention to close and exit the window, simply press and hold Ctrl-Shift while typing U then 4 and then release Ctrl-Shift. Note that the leading 0's do not need to be typed.

ref:

• Ubuntu Unicode composition documentation
• How can I type ASCII characters like Alt + numpad in Windows?
• How can unicode symbols u+2404 ␄ EOT and u+2405 ␅ ENQ be corrected?
• wikipedia.org unicode generation article
• wikipedia.org SO & SI article

Bad Unicode SO glyph in Ubuntu 12.04.