Future Extensibility

This clause provides a high-level overview of the extensibility model for Office Open XML documents, and a description of packaging conventions in the context of DrawingML and PresentationML. Two main constructs are described: extensibility lists (<extLst>/<ext>) and alternate content blocks (<AlternateContent>).

To illustrate certain points, a number of examples refer to versions of a (fictitious) PresentationML consumer/producer called PML. The 2003 version is called PML 2003; the 2007 version is called PML 2007; and so on.