Parents tag - channel/field required?

Let me know if I’m being too specific based on where the development is at..😉

The docs make it sound like the channel/field parameters on the parent tag are optional:

You can get more specific by specifying a channel and a field that you want to check to see if this entry is a child.

But using the parents tag in a template without them netted this error:

Fatal error: Uncaught exception ‘RuntimeException’ with message ‘Parent tag without field parameter.’ in /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Relationships.php:573 Stack trace: #0 /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Relationships.php(391): Relationship_Parser->_unique_entry_ids(Object(QueryNode), Array) #1 /Applications/MAMP/htdocs/gb_backup/system/expressionengine/modules/channel/mod.channel.php(363): Relationship_Parser->query_for_entries(Array) #2 /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Template.php(1295): Channel->entries() #3 /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Template.php(884): EE_Template->process_tags() #4 /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Template.php(453): EE_Template->tags() #5 /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Template.php(235): EE_Template->parse(‘??{embed=”embed…’, false, ”) #6 /Applications/MAMP/htdocs/g in /Applications/MAMP/htdocs/gb_backup/system/expressionengine/libraries/Relationships.php on line 573