code: public function append($a, $b = true, $comparatorCallback = null)
      {
          $this->comparisonList[] = array($a, $b, $comparatorCallback);
          return $this;
      }
docs: Add a new value pair to comparison list
  
  @param mixed $a
  @param mixed|true $b                     If you just provide $a it is compared with a boolean TRUE
  @param null|callable $comparatorCallback If you pass in an optional callback, this callback is used to compare $a and $b.
  The callback should return TRUE if $a and $b are equals or FALSE if not.
  If $a and $b are arrays with a numeric index aka. lists, the callback is
  called for every item in list $a and the item of list $b with the same index.
  
  @return EqualsBuilder
  
  @example
  
  <code>
  echo EqualsBuilder::create()
  ->append(1, 1)
  ->append('equals', 'equals')
  ->append($aArray, $bArray)
  ->append($vo->sameValueAs($otherVo))
  ->append($aVo, $bVo, function ($aVo, $bVo) { return $aVo->sameValueAs($bVo); })
  ->append($aList, $bList, function ($aItem, $bItem) { return $aItem->sameValueAs($bItem); })
  ->equals();
  </code>