source:
  schema:
    constraint: (newData.isString() && newData.val().matches(/^\+(?:[0-9] ?){6,14}[0-9]$/))
  access:
    - location: /
      write: true

expected: {"rules":{".write":"(((newData.isString()&&newData.val().matches(/^\\+(?:[0-9] ?){6,14}[0-9]$/))))",".read":"false"}}