Recently, I read some document on HTTP message from RFC 7230, and I saw the definition of HTTP message:
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body ]
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I understand what the symbol * and [] in this expression mean, but I would like to know which kind of expression the RFC use to define a sequence of characters and the name of this kind of expression. Is this expression called ABNF?