Trying to define application-level cascade in schema file throws Doctrine_Import_Exception:

Example schema.yml:

...

User: 
  columns: 
    id: 
      primary: true
      autoincrement: true
      type: integer(4)
    group_id:
      type: integer(4)

  relations:
    Group:
      cascade: [delete]
...

Building models will throw Doctrine_Import_Exception with message

Invalid schema element named "cascade"