Connector: using references in interfaces

Hi, when I have a reference in my interface:

'My reference': text -> . 'Some collection'[]

How can I get to a value on that collection, is that only possible with a lookup? I would like to do something like this:

let $'My value' = $'context' > 'My reference' . 'Value on some collection'

Yes, this is only possible with a lookup.
Currently only collection uniqueness constraints and number bounds are evaluated by the connector, all other constraints are not yet supported.

What would such a lookup look like? Can you provide an example?

Like this, for instance:

let $'My value' =  $'Item' . 'To' [ $'Item' .'Contactpersoon' ] . 'Name' || ""