How to load the definition of a case type with the CaseType API
It's probably actually easiest to look at the code. CRM_Case_BAO_CaseType::convertDefinitionToXML() gives the list of array elements to set, e.g.

$definition = array(
  'activityTypes' =&gt; array(
    'key1' =&gt; 'value1',
    'key2' =&gt; 'value2',
  ),

  'statuses' =&gt; array(
    'blah1',
    'blah2',
  ),
// etc...
);