title: [A-z0-9]+ regexp matching square brackets
body: <p>I'm struggling with the following regexp</p>
  
  <pre><code>[A-z0-9]+
  </code></pre>
  
  <p>If tested against this string:</p>
  
  <pre><code>||a919238[.--a]asd|
  </code></pre>
  
  <p>it returns <code>a919238[</code>, including the square bracket.. I tried to input <a href="https://www.regex101.com/r/lE6cR8/2">my test case on regex101</a> to understand what's wrong, but the site regex explanation is not helping, probably I'm not able to see my mistake.</p>
  
  <p>Why is the square bracket included in the result?</p>