Vector Markup Language (VML, not to be confused with VRML) is the XML-based vector graphics system that has been present in Internet Explorer for the last eight years. Although not as widely-documented or well-known as its younger cousin, SVG, VML is a capable system with all of the features needed to create dynamic images on the Web client.
Nothing beats an example for discussing technologies. To clarify the modifications to the stylesheet and namespace required by VML, an example is given on a separate page:
Internet Explorer is the only major browser to support VML, so the image won't be visible on other clients. The image is hyperlinked to the Chempedia entry for Oxytocin.
This example's VML was generated with a development version of ChemWriter.