OpenXML :

• https://msdn.microsoft.com/en-us/library/office/gg278330.aspx
• https://msdn.microsoft.com/fr-fr/library/office/gg278335.aspx
• http://openxmldeveloper.org/discussions/formats/f/15/t/317.aspx
• http://openxmldeveloper.org/blog/b/openxmldeveloper/archive/2007/07/29/1834.aspx

Open Document (office:annotation):

• http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1416194_253892949