DSL quereies: filtering by pages

Hey there!
I am trying to create some custom queries form my daily journals but I am facing some issues with the DSL format. I have the following query:

- #+BEGIN_QUERY 
  {
  :query 
  [
    :find (pull ?b [*])
    :in $ ?today
    :where
    (task ?b #{"LATER" "DOING" "WAITING" "NOW"})
    ;; (page ?b #{"urgent"})
    (page ?b #{"urgent"})
  ]
  :inputs [:today]
  }
  #+END_QUERY

But it’s not showing any result. Also, does anyone know a good reference to read for the new query system?
Thanks