 replacing a method on an instance (a feature of JavaScript) or by defining a subclass.
  You should not modify the prototypes of any of the <b>GoJS</b> classes.
</p>
<p>
  In addition to our samples, <b>GoJS</b> provides an <strong><a href="../samples/#extensions">extensions gallery</a></strong>,
  showcasing the creation of custom tools and layouts.
  Those classes and samples are written in TypeScript, available at <code>../extensionsJSM/</code>,
  as ECMAScript/JavaScript modules -- these use the <code>