Rendering hypertext markup language content

A non-transitory computer-readable medium encoding a computer program product operable to cause data processing apparatus to perform operations comprising:

• receiving a document specifying a hierarchy of hypertext markup language (HTML) elements, each HTML element having a representation in a first visual representation of the document;
• translating the HTML elements into a hierarchy of vector object primitives, at least one of the HTML elements being translated into a corresponding vector object primitive;
• generating the first visual representation of the document by rendering the hierarchy of vector object primitives;
• ordering the vector object primitives in the hierarchy of vector object primitives based on relative depth, a first vector object primitive in the hierarchy being above or under a second vector object primitive in the hierarchy;
• inserting a third vector object primitive into the hierarchy of vector object primitives, the third vector object primitive being under at least one vector object primitive in the hierarchy, the third vector object primitive being specified in a document different from the document specifying the hierarchy of HTML elements;
• and
• generating a second visual representation using the third vector object primitive and the hierarchy of vector object primitives, a representation of the third vector object primitive in the second visual representation being at least partially occluded by a representation of the at least one vector object primitive in the hierarchy.

A system comprising:

• a user interface device;
• and
• one or more computers operable to interact with the user interface device and to perform operations comprising:
• receiving a document specifying a hierarchy of hypertext markup language (HTML) elements, each HTML element having a representation in a first visual representation of the document;
• translating the HTML elements into a hierarchy of vector object primitives, at least one of the HTML elements being translated into a corresponding vector object primitive;
• generating the first visual representation of the document by rendering the hierarchy of vector object primitives;
• ordering the vector object primitives in the hierarchy of vector object primitives based on relative depth, a first vector object primitive in the hierarchy being above or under a second vector object primitive in the hierarchy;
• inserting a third vector object primitive into the hierarchy of vector object primitives, the third vector object primitive being under at least one vector object primitive in the hierarchy, the third vector object primitive being specified in a document different from the document specifying the hierarchy of HTML elements;
• and
• generating a second visual representation using the third vector object primitive and the hierarchy of vector object primitives, a representation of the third vector object primitive in the second visual representation being at least partially occluded by a representation of the at least one vector object primitive in the hierarchy.