How are the 'Pages' and 'Start Page' fields supposed to be used?

When I first saw the ‘Pages’ field I assumed it was the range of pages, e.g. 5872–5879, then I noticed the ‘Start Page’ field which I presume is ‘5872’ but then I thought ‘Pages’ might refer to the number of pages in the citation e.g.,

‘Pages’: 7

‘Start Page’: 5972

What is the purpose of the two fields?
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