adding.
Non-Base64 data is escaped using percent-escapes as necessary to make
it valid, and existing escapes are case normalized.</p>
<p>Accessing the individual parts may fail later if they turn out to have
content that can't be decoded successfully as a string, for example if
existing percent escapes represent bytes that cannot be decoded
by the chosen <a href="dart-convert/Encoding-class.html">Encoding</a> (see <a href="dart-core/UriData/contentAsString.html">contentAsString</a>).</p>
<p>A <a href="dart-