Answered Chunk object properties via API. What does 'snippet' field mean when create Chunk object?

$fields = array(
  'name' => 'chunk2015',
  'snippet' => 'snippetName'
);
$chunk = $modx->newObject('modChunk');
$chunk->fromArray($fields);

$chunk->setContent('Some Content');

$content = $chunk->getContent();

$content = $modx->getChunk('ChunkName');

<p>Placeholder one: [[+placeholder1]]</p>
<p>Placeholder two: [[+placeholder2]]</p>

$myPlaceholders = array (
     'placeholder1' => 'value1',
     'placeholder2' => 'value2',
     // etc.
);

$content = $modx->getChunk('ChunkName', $myPlaceholders);