Want a regular expression and its usage

Hi,
can anyone give me the code for the following requirement:

I have one text area. User enters anyhting including a newline character.
using javascript regexp, I should allow only alphanumeric string including newline(\n) character in that. otherwise give an alert message.
Help is highly appreciated.

Thanks & Regards,
Murthy
annavajjhula@yahoo.com

function checkit (thetextinputbytheuser) {
if (/[^a-zA-Z0-9\n]/.test (thetextinputbytheuser)) {
alert ("You may only enter alphanumeric characters");
textboxname.focus();
return false;
}
}

Be aware that this will disallow punctuation such as , ? or !

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