e integer.  For example, the Unicode character for a
musical G-clef ('ùÑû') with rune value 0x1D11E consists of a UTF-16 surrogate
pair: <code>0xD834</code> and <code>0xDD1E</code>. Using <a href="dart-core/String/codeUnits.html">codeUnits</a> returns the surrogate pair,
and using <code>runes</code> returns their combined value:</p>
<pre class="language-dart"><code>var clef = '\u{1D11E}';
clef.codeUnits;         // [0xD834, 0xDD1E]
clef.runes.toList();    // [0x1D11E]
</code></pre>
<p>The String class