tenho esse codigo fonte <span class="grabtn"><a href="javascript:void(0);" onclick="_editUser('FRUS0023431948\x2FEM0012asdasdasdas@of.com', '', '', '', '', '', false, 'f0');FriendGroupsSection.hideNewGroupDiv(0);; return false;" class="btn">

como fica o preg pra pegar isto -=FRUS0023431948\x2FEM0012asdasdasdas@of.com=- ?

$str = "<span class=\"grabtn\"><a href=\"javascript:void(0);\" onclick=\"_editUser('FRUS0023431948\x2FEM0012asdasdasdas@of.com', '', '', '', '', '', false, 'f0');FriendGroupsSection.hideNewGroupDiv(0); return false;\" class=\"btn\">";

if(preg_match_all("#_editUser\(\'(.*?)\'#", $str, $matches)){
    print_r($matches[1]);
}