Username Validation

username.cfm

<cfparam name="form.username" default="">
<cfif form.username is not "">

<cfif reFindNoCase("^([a-z_\d]+)$", form.userName)>
               good
          <cfelse>
               empty or bad chars found 
          </cfif>
          
 
 </cfif>
<cfoutput>
<form action="" method="post">
<input type="text" name="username" value="#form.username#" />

<input type="submit" name="submit" value="submit" />

</form>         
</cfoutput>