In MODX 2.1 and previous releases there is no easy way to do this, but this is already possible in develop (MODX 2.2.0-dev) using the getElement() method that was added in MODX 2.1. This is preferable to using getObject to retrieve a Chunk as it utilizes the parser's sourceCache and prevents unnecessary queries to the database.
<?php
$chunk = $modx->parser->getElement('modChunk', $chunkName);
return $chunk->process($properties);
So in 2.1, you would have to manually get the property set and pass the properties explicitly to the process() method.
In 2.2, you can include PropertySets and Output Filters in the name, just as it would be in the parsing of a tag:
<?php
$chunk = $modx->parser->getElement('modChunk', "{$chunkName}:{$filter}@{$propertySetName}");
return $chunk->process($properties);
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MODX Staff