How to get selector from .html(output)

How to get selector from .html(output)

 How to make it works if #register_user is added by  function Register() ?
  1. $("#register_user").focus(function() {
  2.                $(this).attr("value","");
  3.         });
       Whole script:
  1. <script>
  2.     $(document).ready(function(){
  3.         
  4.         $("#faq").change(onSelectChange);
  5.         $("#LinkBox").focus(function() {
  6.                 $(this).attr("value","");
  7.         });
  8.        
  9.         $('#sign').click(SignIn);
  10.         $('#register').click(Register);
  11.         
  12.         $("#register_user").focus(function() {
  13.                $(this).attr("value","");
  14.         });
  15.        
  16.        
  17.     });
  18.    
  19.     function onSelectChange(){
  20.         var selected = $("#faq option:selected");   
  21.         var output = "";
  22.         if(selected.val() != 0){
  23.             output = "Answer: " + selected.attr('name') ;
  24.         }
  25.         $("#answer").html(output);
  26.     }
  27.    
  28.     function SignIn(){ 
  29.         var output = "";
  30.         output = '<input type="text" id="signin_user" size="8" maxlenght="8" value="Login" class="signin_user"><input type="password" id="signin_password" size="8" maxlenght="8" value="Password" class="signin_password"><input type="submit" value="Sign In" class="signin_send"/>';
  31.         $("#panel_left").html(output);
  32.     }
  33.    
  34.     function Register(){ 
  35.         var output = "";
  36.         output = '<input type="text" id="register_user" size="8" value="e-mail" class="register_user"><input type="text" id="register_password" size="8" value="password" class="register_password"><input type="text" id="register_password_verification" size="8" value="password verification" class="register_password_verification"><input type="submit" value="Register" class="register_send"/>';
  37.         $("#panel_left").html(output);
  38.     }
  39.    
  40. </script>