title: What does the 'k' prefix indicate in Apple's APIs?
body: <p>I've run across many examples of Core Foundation variables named <code>k</code> + <code>someVariableNameHere</code> or <code>k</code> + <code>APILibraryName(2Char)</code> + <code>someVariableNameHere</code>.  What does this prefix <code>K</code> indicate? </p>
  
  <p>Examples include:</p>
  
  <p><code>kGLPFAStereo</code><br>
  <code>kCollectionLockBit</code><br>
  <code>kSetDebugOption</code></p>