How is "--" changed to "—" within Mail, TextEdit…? I just incidentally discovered that within Mail, TextEdit when typing two dashes in a row, the string "--" is instantaneously changed to "—" (i.e. a long dash).

This magic is mostly loathsome when you need to type exactly "--",
you didn't notice this magic and wasted hours searching why a correct syntax isn't where you typed it. With small fonts this magic change is hard to notice.

This function doesn't exist on Lion and Mountain Lion.

This magic but as unwanted as ununderstood feature raises 3 questions.



Where is this function configured?

How may I get rid of it?

Is this magic useful?
Edit > Substitutions > Untick "Smart dashes". Then relaunch "TextEdit". Same with "Mail".



To your third q: It is simply more beautiful. Personally I don't like when people type long dashes by using two short ones.

A tip: you can type long one even with "smart dashes" disabled with Option+- (short dash).