UTF-8 can never replace Latin-1 as the go-to US-ASCII superset, because, as a variable-length encoding, it cannot use the important size check in equality comparisons with UTF-16 to avoid having to iterate the whole string data. Mention that. UTF-8 only makes sense in a UTF-8-only environment where the size check works again. As long as our preferred charset is UTF-16, Latin-1 must be the preferred US-ASCII wrapper. Pick-to: 6.4 6.3 6.2 Change-Id: Ibe52cfc0c9fce0e7aaacd4cd8d6361e8d8bdee3d Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>