Newbie question: machine actions

[Dan V.]

Hi.  I'm wondering what an embedded action in a machine without a (>,
$, @ %) symbol means.  For example, in cppscan.rl identifiers are
matched with:

    # Identifiers
    ( [a-zA-Z_] [a-zA-Z0-9_]* )
        {token( TK_Id );};

On what condition does token() get called?