User documentation is in la section intitulée « Intervalle harmonique ».

Here is a minimal lesson file:

header {
  module = harmonicinterval
  version = "3.1.4"
  title = "Seconds"
  intervals = 1, 2
  test = "3x"
  test_requirement = "90%"
}

Additional variables you can put in the header. Click on the link to get an explanation: