9. A system comprising: a processor; and computer storage media having computer-executable instructions stored thereon that when executed by the processor implement an electronic document editor comprising: a highlight rendering services component including a highlight rendering services interface that provides one or more methods to enable an editor extension to control which section of an electronic document is highlighted on a screen and to control a style of the highlight, the editor extension determining a visual aspect of the highlight without altering the electronic document and the highlight rendering services component determining non-visual functional aspects of the highlight; a designer extensibility mechanism; a plurality of designers, wherein the designers communicate with the electronic document editor through the designer extensibility mechanism and through the highlight rendering services component; a designer registry containing respective entries for the designers, wherein the entries are arranged in sequential order; and an event routing controller adapted to route events related to the highlight rendering services component to at least one of the designers based at least in part on the sequential order of the entries in the designer registry.
9. A system comprising: a processor; and computer storage media having computer-executable instructions stored thereon that when executed by the processor implement an electronic document editor comprising: a highlight rendering services component including a highlight rendering services interface that provides one or more methods to enable an editor extension to control which section of an electronic document is highlighted on a screen and to control a style of the highlight, the editor extension determining a visual aspect of the highlight without altering the electronic document and the highlight rendering services component determining non-visual functional aspects of the highlight; a designer extensibility mechanism; a plurality of designers, wherein the designers communicate with the electronic document editor through the designer extensibility mechanism and through the highlight rendering services component; a designer registry containing respective entries for the designers, wherein the entries are arranged in sequential order; and an event routing controller adapted to route events related to the highlight rendering services component to at least one of the designers based at least in part on the sequential order of the entries in the designer registry. 17. The system of claim 9 , further comprising an interface to enable the editor extension to control one highlighted section of a document from a group of highlighted sections of the document.