title: Validating a string rather than character set
body: <p>I'm validating user input, but it fails because it checks for any character in the character set as well.</p>
  
  <p>How to assure that I can accept URI like:</p>
  
  <pre><code>e/1test1
  page1/2test2
  p/3test3
  pag/4test4
  test/63tedddddst/test5
  </code></pre>
  
  <p>but not when 'page' exist as a first word followed by '/':</p>
  
  <pre><code>page/test7
  </code></pre>
  
  <p>The expression:</p>
  
  <pre><code>^([^page].+?\/?)$
  </code></pre>
  
  <p><a href="https://regex101.com/r/zP0tQ3/1" rel="nofollow">https://regex101.com/r/zP0tQ3/1</a></p>