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The characters a command shell treats as grammar rather than as text. Every one of them already exists in the catalogue as a typographic mark, and these records describe something the punctuation records cannot: what a shell does with the character. POSIX standardises the set, but it standardised a notation that already existed rather than inventing one, which is why the records read as documented practice that a specification later pinned down.
A vertical bar joining one command's output to the next command's input.
A rightward angle bracket sending a command's output into a file.
A doubled rightward bracket adding output to the end of a file.
A leftward angle bracket feeding a file into a command.
An asterisk standing for any run of characters in a filename pattern.
A hash and exclamation mark naming the interpreter for a script.
A hash making the rest of a line invisible to the interpreter.