Constructor. If there is a document structure tree,
this fills in the appropriate information. If there isn't,
it does nothing. Call isPresent() to determine whether
there is a document structure tree. A PdfInvalidException may be
thrown if there is a structure tree but it is invalid.
module - The PdfModule under which we're operating
Constructor with transient flag. Calling this can save a lot of memory
if the tree is being validated as it's built (which happens to be the
only case, but I don't want to throw out the more general code).
Dereference a name in the role map.
If there is no role map, or if the parameter is not
mapped by the role map, the original parameter will
be returned. The string will be looked up through
multiple levels in the role map. The maximum number
of levels is limited to 50, in case of circular
mappings. The value returned will be null if the
role map contains invalid data or the limit of 50
lookups is reached.