_start_diff example

  public function format(Diff $diff) {
    $xi = $yi = 1;
    $block = FALSE;
    $context = [];

    $nlead = $this->leading_context_lines;
    $ntrail = $this->trailing_context_lines;

    $this->_start_diff();

    foreach ($diff->getEdits() as $edit) {
      if ($edit->type == 'copy') {
        if (is_array($block)) {
          if (sizeof($edit->orig) <= $nlead + $ntrail) {
            $block[] = $edit;
          }
          else {
            if ($ntrail) {
              $context = array_slice($edit->orig, 0, $ntrail);
              $block[] = new DiffOpCopy($context);
            }