title: Regex: a certain numeral at a certain place
body: <p>How can I write a regex expression that checks a certain numeral at a certain place?</p>
  <p>For example, if I want to have regex for only numerals, length 7 - I will write
  something like</p>
  <pre><code>^[0-9]{7}$
  </code></pre>
  <p>But how can I make that the 4th digit is always 1?</p>
  <p>Example:</p>
  <pre><code>0031000 true
  
  9991999 true
  
  9992999 false 
  </code></pre>