The version attribute always has the value 1.0. If XML 1.1 is released in the future (and it may not be), this will probably also be allowed to have the value 1.1. Regardless, you should always use XML 1.0, never version 1.1. XML 1.0 is more compatible and more robust, and it offers all the features XML 1.1 does. Item 3 discusses this in more detail.