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Gets or sets a format string used to format the page ranges of occurrences of index entries in the generated index.
The default is "{0}-{1}".
public string PageRangeFormat { get; set; }
When an index entry occurs on consecutive pages in a document (e.g. on pages 3, 4 and 5), those occurrences are collapsed into a range ("3-5" in that case). PageRangeFormat is used to format those ranges.