Discovered this in
The standard, section 6.10, <window function>.
syntax rules says:
7) b) The window framing clause of WDX shall not be present.
MariaDB: ok (framing ignored)
PG: Ok (framing ignored)
Oracle: ORA-00907: missing right parenthesis
MS SQL: The function 'rank' may not have a window frame.
I think, it is better to follow the standard and return an error, then to accept the frame definition and then silently ignore it.