I can not use some characters in markers

[aoreinoso]

Why can not I use - as a marker?
$log.error('The marker can't use a "-" on his key name: "' + newName + '".');
I have commented

//if (newName.search('-') !== -1) {
 // $log.error('The marker can\'t use a "-" on his key name: "' + newName + '".');
 //continue;
//}

in my app and I have not noticed any errors

Thanks in advance