The value relation widget filter expression can now use two
new functions/variables that have access to the current
values and geometry of the form being edited.
This allows for dynamic filtering (drill-down) as explained
in the crowdfunding page:
https://north-road.com/drill-down-cascading-forms/
The new functions/variables are:
Function:
get_current_form_field_value( 'FIELD_NAME' )
Variable:
@current_form_geometry
