how to combine the error message from jquery validation. for example:

messages: {
    first_name: { required: "Please enter your first name." },
    email: {
         required: "Please enter a valid email address.",
         remote: "Email has been registered."
    },
    username: {
         required: "Please enter username.",
         remote: "Username has been registered."
    }
 },

Desired message will be like this:

Please enter your first name, a valid email address and username

or

Please enter your first name and username, email has been registered etc.