I have seen some writing where people have a list or a figure in writing and they will write something like this:
The information is provided in Image 3:-
Is that correct? Is this a British style?
According to Nick Marten's The Secret History of Typography in the Oxford English Dictionary, a colon followed by a dash is a typographical mark that the OED refers to as the dog's bollocks:
Marten does not further elaborate on its purported usage, but others do:
Modern style guides seem intent on banishing its usage to history. For example, the University of Sussex has a strong opinion on the matter:
I'd love to find some examples in print, but as you can imagine:— it's extraordinarily difficult to google.
It's correct, because it is a recognised, well-known usage. However, it is redundant, and in most situations not the best or right usage. I would only use it where there is an established convention for its usage, such as in certain court documents.
English documents written in India often use
(These quotes are merely illustrative and not meant to prove that
I do not know why
The interested reader who seeks additional examples may wish to consult this Stack Exchange Data Explorer query, which identifies instances of
Looking around this page, colon + hyphen appears to be common to a number of Commonwealth and British territories, though there are exceptions to that rule (e.g. Phillipines).
Usage in legislation would seem to indicate that it is indeed "proper" to use punctuation in this way. The fact that its use is mainly (though not exclusively) in countries with a British connection suggests that it may be more a British style than a non-British one.
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