The opening sentence of Chapter Twelve of SM Stirling's On The Oceans Of Eternity informs us that Tarmendtal enjoys trading, taking tribute and showing the flag. Thus, this is his pov. The second sentence continues that it was a relief to be in open prairie. This is still Tarmendtal's pov. However, an aside informs us that the prairie is:
"... - what another history would have come to call the Sacramento Valley -..." (p. 250)
This is background information provided by the omniscient narrator from outside Tarmendtal's pov. An exercise for a writer would be to find a way to convey this information without stepping outside the viewpoint character's pov. In Doctor Mirabilis, James Blish resorted to an afterword to inform us that, in one scene, Roger Bacon had had an experience with what we call "ether."
On The Oceans Of Eternity keeps us in suspense by frequently changing its pov.