title: Regular expression for filtering similar characters
body: <p>I'm trying to construct a regular expression to implement the following restriction:</p>
  
  <blockquote>
    <p>The value may be of any length, but may not contain similar letters/numbers which may cause confusion when printed. E.g., 1 (the numeric), I (an upper-case Latin i) and l ( a lower case Latin L) look similar; there may be other such examples</p>
  </blockquote>
  
  <p>I've tried a few things but can't get it to work, any help would be much appreciated: thanks.</p>
  
  <p>For example: I could have <code>Linux1</code> but not <code>LINUX1</code> or <code>linux1</code></p>