Should I Use std.ascii.isWhite or std.uni.isWhite?

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I'm confused about which isWhite function I should use. Aren't 
all chars in D (char, wchar, dchar) unicode characters? Should I 
always use std.uni.isWhite, unless I'm working with bytes and 
byte arrays? The documentation doesn't give me much to go on, 
beside "All of the functions in std.ascii accept unicode 
characters but effectively ignore them. All isX functions return 
false for unicode characters, and all toX functions do nothing to 
unicode characters."