title: Regex for bunch of choices without any order
body: <p>I'm trying to create a JAVA regex to test if specific options are set. At the moment I have <code>[ks]?[zx]?[ap]?</code> so it is either k, s or nothing, then z, x or nothing and at last a, p or nothing.</p>
  
  <p>The only problem with this regex is it works only in this one order but it should work with all orders, because <code>kza</code>, <code>azk</code>, <code>zka</code>, <code>kaz</code>, <code>akz</code> and <code>zak</code> do the same thing.</p>