A usual entry looks like this:
<?php
array(6) {
  'file' =>
  string(87) "DbSelector.php"
  'line' =>
  int(171)
  'function' =>
  string(5) "error"
  'class' =>
  string(42) "LoggingService"
  'type' =>
  string(2) "::"
  'args' =>
  array(1) {
    [0] =>
    string(27) "Connecting to DB: unittests"
  }
}
?>

Be warned though that 'file' and 'class' do not reference the same thing!
'file' means which file calls the next step.
'class' is the next step being called.

So 'file' is the caller, 'class' is the callee.