title: Allow only numbers with only specific alphabets in textbox
body: <p>i have a text box in html, i want to allow user to only input following range</p>
  <p>0-9 and NA</p>
  <p>there are two cases<br />
  1: user inputs range form 0-9 numbers and<br />
  2: user inputs only NA (NA denotes Not applicable)</p>
  <p>how could i allow user to do this</p>
  <p>I try following code but it does not work</p>
  <pre><code>&lt;input type = &quot;number&quot; autocomplete=&quot;off&quot; class = &quot;form-control&quot;  name=&quot;Personal_Weapons_Price&quot; id = &quot;Personal_Weapons_Price&quot;   required  onkeyup=&quot;this.value = this.value.toUpperCase();&quot; pattern=&quot;[^0-9NA]+&quot; /&gt;
  </code></pre>