those are treated as two code points.  For simplicity, this document
will use the unqualified term <i>character</i> to refer to a Unicode code point
in the source text.
</p>
<p>
Each code point is distinct; for instance, upper and lower case letters
are different characters.
</p>
<p>
Implementation restriction: For compatibility with other tools, a
compiler may disallow the NUL character (U+0000) in the source text.
</p>
<p>