What is the'function'keyword used in some bash scripts- What is the 'function' keyword used in some bash scripts?

problem ：

For example: Bash-Prog-Intro-HOWTO for example ： Bash-Prog-Intro-HOWTO

function foo() {}

I make search queries in info bash and look in releted chapters of POSIX for function keyword but nothing found. I am here info bash Search query , And in POSIX Found in the rewritten chapter of function keyword , But nothing was found .

What is function keyword used in some bash scripts? In some bash In the script function What is the keyword ？Is that some deprecated syntax? Is that some grammar that doesn't approve of using ？

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Solution ：

Reference resources ： https://stackoom.com/en/question/XDZq