Returns zero-based position of the bookmark with the specified index.
property Bookmarks [Index: integer]: integer;
If bookmark with the specified index does not exist, Bookmarks[Index] returns -1, otherwise Bookmarks[Index] returns position of the bookmark.
If bookmark exists, writing to Bookmarks property will change position of the bookmark. If assigned value is -1 and bookmark exists, this bookmark will be destroyed.
If no bookmark has been found and assigned value is not -1, new TBookmark object will be created with the specified index and position. After creating bookmark OnSetBookmark event occurs, in which you can adjust properties of the new bookmark object.