bkl (4 bytes): A BKL specifying further information about the bookmark.
cDepth (4 bytes): An integer specifying the number of bookmarks in the document of the same type as the bookmark associated with this BKLD, the ranges of which overlap the limit of this bookmark range. To increment the count, a bookmark MUST meet the following constraints:
The bookmark BKLD occupies the PlcBkld containing this BKLD
The bookmark limit CP (cpL) and start CP (cpS), as defined in the specification of that PlcBkld and the PlcBkfd it is paired with, satisfy the following in relation to the CP (cpCur) marking the limit of the bookmark of this BKLD
Because BKLD is only associated with structured document tag bookmarks, cDepth can be rephrased more simply as the zero-based count of other structured document tag bookmarks in the file that contain the bookmark associated with this BKLD.