PYK: The empty string is a string containing no characters. Because of Tcl's copy-on-write implementation of values, there is precisely one empty string. In a Tcl script, there are exactly three notations for the empty string: {}, "", and [some_command_that_returns_the_empty_string_including_possibly_no_command_at_all].
AMG: Actually, you can obtain empty string by typing [].
PYK :P
See also: is_empty