6.4.6 Punctuators
….@H_403_3@

3 In all aspects of the language,the six tokens@H_403_3@

<: :> <% %> %: %:%:@H_403_3@

behave,respectively,the same as the six tokens ⁷⁹⁾@H_403_3@

[ ] { } # ##@H_403_3@

except for their spelling.⁸⁰⁾@H_403_3@

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79) These tokens are sometimes called ‘‘digraphs’’.@H_403_3@

80) Thus [ and <: behave differently when ‘‘stringized’’ (see 6.10.3.2),but can otherwise be freely interchanged.@H_403_3@

作为附注,C标准阐述了以下术语：@H_403_3@

The term “digraph” (token consisting of two characters) is not
perfectly descriptive,since one of the alternative preprocessing-tokens is %:%: and of course several primary tokens contain two
characters. Nonetheless,those alternative tokens that aren’t lexical keywords are colloquially known as “digraphs”.@H_403_3@

根据Digraphs and trigraphs：@H_403_3@

In 1994 a normative amendment to the C standard,included in C99,supplied digraphs as more readable alternatives to five of the trigraphs. ….@H_403_3@

Unlike trigraphs,digraphs are handled during tokenization,and any digraph must always represent a full token by itself,or compose the token %:%: replacing the preprocessor concatenation token ##. If a digraph sequence occurs inside another token,for example a quoted string,or a character constant,it will not be replaced.@H_403_3@