var digitSurroundedBySpace = /SDS/;
document.writeln("1234567AB".search(digitSurroundedBySpace));

var digitSurroundedBySpace = /DS/;
document.writeln("1234567AB".search(digitSurroundedBySpace));

var digitSurroundedBySpace = /SDS/;
document.writeln("1234567AB".search(digitSurroundedBySpace));
//  index:        012345678
//  match:              ^

var digitSurroundedBySpace = /DS/;
document.writeln("1234567AB".search(digitSurroundedBySpace));
//  index:        012345678
//  match:               ^