code: def read_xref_from(self, parser, start, xrefs):
          
          parser.seek(start)
          parser.reset()
          try:
              (pos, token) = parser.nexttoken()
          except PSEOF:
              raise PDFNoValidXRef('Unexpected EOF')
          if self.debug:
              logging.info('read_xref_from: start=%d, token=%r' % (start, token))
          if isinstance(token, int):
              # XRefStream: PDF-1.5
              parser.seek(pos)
              parser.reset()
              xref = PDFXRefStream()
              xref.load(parser)
          else:
              if token is parser.KEYWORD_XREF:
                  parser.nextline()
              xref = PDFXRef()
              xref.load(parser)
          xrefs.append(xref)
          trailer = xref.get_trailer()
          if self.debug:
              logging.info('trailer: %r' % trailer)
          if 'XRefStm' in trailer:
              pos = int_value(trailer['XRefStm'])
              self.read_xref_from(parser, pos, xrefs)
          if 'Prev' in trailer:
              # find previous xref
              pos = int_value(trailer['Prev'])
              self.read_xref_from(parser, pos, xrefs)
          return
docs: Reads XRefs from the given location.