custom Field
It is possible to filter the tracker items by user defined fields. To use this filter you must define the ID of the tracker in which you want to use the filter, since the custom fields may be different in each tracker. The property name of a field is available on the tracker configuration page.
'1234.customField[1]' = 1 //where 1234 the id of the tracker and the customField[1] is the property name of field
'1234.choiceList[1]' = 'Option1'