Microsoft made available the online version of the Visio 2010 SDK documentation. This documentation, which also shipped with Visio 2010 SDK download, is intended to help developers working with the Visio APIs, ShapeSheet and XML. It contains the following Visio developer references: "Automation Reference, Save as Web Reference, ShapeSheet Reference, Viewer Reference, and XML Schema Reference".
For Visio Services developers, documentation is available online as well as offline via Microsoft SharePoint 2010 SDK. This documentation is divided into Visio Services in SharePoint Server overview articles and Visio Services Class Library technical information, and covers following topics: "Visio Services ECMAScript API, and Visio Custom Data Providers".