JointJS exports three global variables, the joint namespace, the V variable and the g variable (that is described later in the Geometry section). The V variable is a function of a little SVG helper library that we call Vectorizer. The reason why this library sits in its own namespace and not inside the joint namespace is that it can be used completely standalone, even without JointJS. It is a very helpful library making life easier when dealing with SVG. You can think of it as of a very lightweight jQuery for SVG. If you want to use Vectorizer as a standalone library, see the download page that contains both the development and minified versions.