This property represents the "Limits" entry of the name tree
node dictionary object.
It is defined as part of the PDF 1.0 specification.
It is an Array containing two strings representing the lower and
upper bounds of the tree.
The first string represents the lowest key in the EntryNames entry of this or any child
The second string represents the highest key in the EntryNames entry of this or any child
For definitive details see:.
The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 36,