if $($inputElement$.$id $==$ "bookingreference"$)\{$

$//^$$ $=$ anchors, $[$a$-$zA$-$Z$]=$ letters, $\{3\}=3$ of them, $-=$ a hyphen, $[0-9]=$ digits, $\{5\}=5$ of them

pattern $=/^[$a$-$zA$-$Z$]\{3\}-[0-9]\{5\}$$$/$;

feedback $=$ "Only valid booking references are permitted";

$\}$