能否只用一条正则表达式验证密码两种类型组合

var pwd_default_regexp = /^[a-z]{6,20}$|^[A-Z]{6,20}$|^[0-9]{6,20}$/;

var pwd_normal_regexp = /^(?=.*[0-9])(?=.*[a-z])[0-9a-z]{6,20}$|^(?=.*[0-9])(?=.*[A-Z])[0-9A-Z]{6,20}$|^(?=.*[a-z])(?=.*[A-Z])[a-zA-Z]{6,20}$/;

var pwd_plus_regexp = /^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])[0-9a-zA-Z]{6,20}$/;