title: How does one use NSDateFormatter's isLenient option?
body: <p>I can't seem to find any info on this flag, on StackOverflow or elsewhere on the web.  Apple's own documentation only says:</p>
  
  <blockquote>
    <p>If a formatter is set to be lenient, when parsing a string it uses heuristics to guess at the date which is intended. As with any guessing, it may get the result date wrong (that is, a date other than that which was intended).</p>
  </blockquote>
  
  <p>Maybe I'm misunderstanding how this is supposed to work, but I can't get it to work at all.  My guess was something like this (with a relatively easy date to parse):</p>
  
  <pre><code>&gt; import Foundation
  &gt; let df = DateFormatter()
  &gt; df.isLenient = true
  &gt; df.date(from: "12:00 1/1/2001")
  $R0: Date? = nil
  </code></pre>
  
  <p>No matter what I try, I get nil.</p>
  
  <p>I also see there's a <code>doesRelativeDateFormatting</code> flag, which claims to support phrases such as “today” and “tomorrow”", but that doesn't seem to do anything, either:</p>
  
  <pre><code>&gt; df.doesRelativeDateFormatting = true
  &gt; df.date(from: "today")
  $R1: Date? = nil
  </code></pre>
  
  <p>Any ideas?</p>