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  New/Additional Comment:
  Description:
  ------------
  When you call undefined global function inside namespace, the error message contains namespace, which is usually confusing.
  Example: Suppose that I have not enabled extension 'json' by mistake. Now this code
  <?php
  namespace Nette;
  echo json_encode($x);
  ?>
  leads to error "Call to undefined function Nette\json_encode()". The better message should be "Call to undefined function json_encode()".
  I know how works function name resolution, but consider these points:
  1) functions are used in namespaces only rarely
  2) functions are usually called without leading slash, i.e. not fully qualified
  3) both error messages are correct, none is more correct than the other
  So it is much more likely that I call a global function, so it would be preferable to use message WITHOUT namespace.
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  In my opinion the current error message is preferable over your
  suggestion, because looking for a global function (or constant for
  that matter) is only a *fallback*.