title: Should we consider using range [a-z] as a bug?
body: <p>In my locale (et_EE) <code>[a-z]</code> means:</p>
  
  <pre><code>abcdefghijklmnopqrsšz
  </code></pre>
  
  <p>So, 6 ASCII chars (<code>tuvwxy</code>) and one from Estonian alphabet (<code>ž</code>) are not included. I see a lot modules which are still using regexes like </p>
  
  <pre><code>/\A[0-9A-Z_a-z]+\z/
  </code></pre>
  
  <p>For me it seems wrong way to define range of ASCII alphanumeric chars and i think it should be replaced with:</p>
  
  <pre><code>/\A\p{PosixAlnum}+\z/
  </code></pre>
  
  <p>Is the first one still considered idiomatic way? Or accepted solution? Or a bug?</p>
  
  <p>Or has last one some caveats?</p>