这句话是什么意思啊 求解

[bird_cat]

求解：
The size for strings has two factors: the number of units allotted and the type of units allotted.
A string of three characters (derived from the character set) cannot fit in a string of three bytes,
and more naturally a string of three characters cannot fit in a string of two characters. Any attempt
to make that type of assignment raises an ORA-06502, which means a character string buffer is
too small to hold a value

我根据以上内容做了个实验

DECLARE
SUBTYPE code IS VARCHAR2(3 byte);
c VARCHAR2(3 CHAR) := 'ABC';
d CODE;
BEGIN
d := c;
END;
/
没有报错，按照上面的说法应该报ORA-06502的