Should an em dash have spaces around it?
I always thought it shouldn't have spaces, but I recently read that in some cultures it is common to include spaces:
[...] the "space, en dash, space" sequence is the predominant style in German and French typography.
I have also heard of the use of a hair space on either side of the dash in some contexts:
[...] an em dash should always be set closed, meaning it should not be surrounded by spaces. But the practice in some parts of the Enlgish-speaking world [...] sets it open, separating it from its surrounding words by using spaces or hair spaces (
U+200A) when it is being used parenthetically.
In fact, we can see this hair space on either side being desired outcome here.
Conversely, some say it's merely a matter of style/personal preference.
Is there a rule or tradition I should follow? If, in the context described above, set open is preferable, should I use a normal space (U+0020) or a hair space (U+200A)?