How does : <<'END' work in bash to create a multi-line comment block?

Question

I found a great answer for how to comment in bash script (by @sunny256):

#!/bin/bash
echo before comment
: <<\'END\'
bla bla
blurfl
END
echo af         


        

Answer 1

It is called a Here Document. It is a code block that lets you send a list of commands to another command or program

The string following the << is the marker determining the end of the block. If you send commands to no-op, nothing happens, which is why you can use it as a comment block.