I can define fake slant for a font with

    \definefontfamily[mainface][rm][My Fancy Font][sl=features:slanted]

How can I do it with \definefallbackfamily?

According to
https://wiki.contextgarden.net/index.php?title=Command/definefallbackfamily
, the following should work, but it actually doesn't:

    \definefallbackfamily[mainface][rm][My Fancy
Font][preset={range:chinese},sl=features:slanted]

Besides, the wiki page lists an option `range=...` in the last bracket, but
what's actually used is `preset=range:...`. Are they mistakes?