| path | The PropertyPath | 
| startIndex | The zero-based index where the sub path should start. | 
PropertyPath A new PropertyPath
Returns a new PropertyPath containing the PropertyPathPart starting at the given start index.
| path | The PropertyPath | 
| startIndex | The zero-based index where the sub path should start. | 
| length | The number of parts to include. | 
PropertyPath A new PropertyPath
Returns a new PropertyPath containing the given number of PropertyPathPart starting at the given start index.