Each page in a PDF document shall be identified by an integer page index that expresses the page’s relative position within the document. In addition, a document may optionally define page labels (PDF 1.3) to identify each page visually on the screen or in print. Page labels and page indices need not coincide: the indices shall be fixed, running consecutively through the document starting from 0 for the first page, but the labels may be specified in any way that is appropriate for the particular document.