Increases the reference's counter of links on the document.
Role:
The life cycle of the document is not managed by the AddRef/Release
mechanism. The mechanism of reference/unreference is CATLockDocument to increase the
count of links on the document, and
CATUnLockDocument to decrease its count. Such as Release, CATUnLockDocument closes the document in the session when the counter is null.
When do you use this mechanism ?
interactive mode, if your class keeps a pointer on a
CATDocument, use this method to add a link, and when the pointer is no longer needed use the
CATUnLockDocument method