Netgen Class List Datatype is an eZ Publish extension that provides a datatype to select and store a list of content classes.
Suppose you are developing a Category class that has attributes which parametrise how fetching of children works. You would add a class_filter_array attribute (which is of ngclasslist datatype provided by the extension) to your Category class and would use it in the following way in the code:
{def $children = fetch(
'content', 'list',
hash(
'parent_node_id', $node.data_map.parent_node_id.content,
'class_filter_type', $node.data_map.class_filter_type.content,
'class_filter_array', $node.data_map.class_filter_array.content.class_identifiers
)
)}