title: Excel 2010 Data Validation allow specific layout
body: <p>I want to apply data validation to reference numbers, to force the following layout (ideally uppercase only):</p>
  
  <p><strong>XX_NNX-XX_NNN_NN-XXX</strong></p>
  
  <p>X = Numbers</p>
  
  <p>N = Letters</p>
  
  <p><em>Ex: 12_AB1-23_ABC_AB-123</em></p>
  
  <p>The following custom formula allows all of it except for numbers - is there any workaround for this?</p>
  
  <p>I don't want to use * since it allows for more characters than I want.</p>
  
  <p><code>=COUNTIF(A1,"??_???-??_???_??-???")</code></p>