At a point in time between May and June Microsoft has released the first version of a new specification called Application Virtualization (App-V) Volume Format.
The 31-pages still-unreleased document, published by Ruben Spruijt of Project Virtual Reality Check (VRC) fame, describes in details the file based file-system used by App-V containers, giving enough details to support it in 3rd party commercial and free applications.
Microsoft already published another App-V specification dedicated to the file format in February.