This isn’t restricted to ‘page’: there’s a whole set of PDF fragment identifiers [0,1]. Most notably ‘zoom’, ‘view’ and named destinations, but there are others.
Writing links by hand is rather cumbersome, though, they ought to be better exposed in PDF viewers. It certainly doesn't help adoption when the list of allowed parameter values is locked in a proprietary spec!
view=<keyword>,<position>
The arguments correspond to those found in [ISOPDF2] 12.3.2.2
"Explicit destinations". <keyword> is one of the keywords defined
in [ISOPDF2] "Table 149: Destination syntax" with appropriate
position values.
[ISOPDF2] ISO, "Document management -- Portable document format --
Part 2: PDF 2.0", ISO 32000-2:2017, 2017.
PDF is open since 1993, if that's the spec you mean
EDIT: If it's important that it's the actual standardized version rather than the final draft then you can get it for free here: https://www.pdfa-inc.org/product/iso-32000-2-pdf-2-0-bundle-...
(Strictly speaking it's the 2020 revision which incorporates some errata. I don't know if the final standardized 2017 version was made freely available)