Template:Mdashb
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Creates a "mdash breakable" i.e. an mdash followed by a zwsp (zero-width space).
Many browsers will not break a line after an mdash (and they never break before an mdash) so word{{mdash}}word becomes a very big unbreakable sequence, causing bad line breaks. Coding word{{mdashb}}word is the equivalent of word{{mdash}}{{zwsp}}word. A zwsp (zero-width space) signals the browser that it's OK to break at that point.