source:
  functions:
    - f(a): data.a       #should be substituted
    - g(a): newData [a]  #should not be substituted

  schema:
    constraint: f("g") + g("h")

  access:
    - location: /
      write: true

expected: {"rules":{".write":"((data.child('a')+newData.child('h')))",".read":"false"}}