* a field starting with '&' or '|' should refer to a sequence type

  the semantic is then that the object value (expected to be a list)
  should contain all (&) or any (|) value specified in the corresponding
  filter value. See other examples below.
    example : filter = { '|role_ids' : [ 20, 40 ] }
    example : filter = { '|roles' : ['tech', 'pi'] }
    example : filter = { '&roles' : ['admin', 'tech'] }
    example : filter = { '&roles' : 'tech' }