Whether or not c is a whitespace character. That includes the space, tab, vertical tab, form feed, carriage return, and linefeed characters.
assert( isWhite(' ')); assert( isWhite('\t')); assert( isWhite('\n')); assert(!isWhite('1')); assert(!isWhite('a')); assert(!isWhite('#')); // N.B.: Does not return true for non-ASCII Unicode whitespace characters. static import std.uni; assert(std.uni.isWhite('\u00A0')); assert(!isWhite('\u00A0')); // std.ascii.isWhite