What is a "comma expression"?

[rempas]

On Sunday, 10 October 2021 at 12:13:47 UTC, Elmar wrote:
>
> Hello rempas.
>
> The comma-operator `,` is like `;` but results in an expression 
> value, not a statement like `;` would. The left side of `,` is 
> executed like a statement and the value of the right side of 
> `,` is returned. Comma-expressions are merely used to pack 
> additional instructions into places where only expressions are 
> allowed.
>
> [...]

Thanks, that's the second time you are helping me today!