Factorio Forums

Normally when placing a blueprint, the Unsorted tab that contains the literal parameter types 0-9 is not visible, so those types can't be used in filter/request slots. However, immediately after clicking "Create blueprint", if you place the blueprint object in the cursor into the world, it allows you to click on a literal parameter type.

So you can have a slot with a parameter type in the world, like so.

Thanks for the report. This is Not a bug. I am not seeing any value added in forcing those parameters to never be on real entities, especially since you can go to interface settings and enable "Show parameters in selection lists" to intentionally configure real entities with parameters without using the blueprints and only after entities are pre-configured with parameters create a blueprint out of them.