The types char and str hold textual data.
A value of type char is a Unicode scalar value (i.e. a code point that
is not a surrogate), represented as a 32-bit unsigned word in the 0x0000 to
0xD7FF or 0xE000 to 0x10FFFF range. A [char] is effectively a UCS-4 / UTF-32
string.
A value of type str is a Unicode string, represented as an array of 8-bit
unsigned bytes holding a sequence of UTF-8 code points. Since str is a
dynamically sized type, it is not a first-class type, but can only be
instantiated through a pointer type, such as &str.