gistfile1.php

<?php

array(
'invitees' => array(
	'name' => 'invitees',
	'source' => 'non-db',
	'type' => 'link_field',
	'link' => 'meeting_invitees',
	'fields' => ['id', 'name', 'picture', 'status']
	'sort_on' => 'name'
)
);

array(
    'layout' => 'collection-subpanel',
    'label' => 'LBL_WEEK_ACTIVITIES_SUBPANEL',
    // This subpanel def resides in PARENT module, e.g. Calendar
    // This defines headers, footers, etc. and also the field list
    'override_subpanel_list_view' => 'subpanel-for-calendar',
    'context' => array(
	'collection' => 'meeting_invitees',
	'links' => array(
		// Optional override for each link, specific for this subpanel
		// If not used, fields from layout in the main definition are used
        	'calls' => array(
        		// This subpanel def resides in Calls
                	'override_subpanel_list_view' => 'subpanel-for-calendar',
        	),
     	),
     ),
)


$a = [
    'meeting_invitees' => array(
        'name' => 'meeting_invitees',
        'source' => 'non-db',
        'type' => 'collection',
        'vname' => 'LBL_MEETING_INVITEES',
        'links' => array(
            'calls', 'meetings',
            array( 
                'name' =>  'tasks',
                'field_map' => array(
                     // virtual field => real field
                         'date_end' => 'date_due',
                     )
                ),
            ),
        ),
        'sort_on' => 'date_end'
    ];