Why Xml describes XML, and why it is suitable for the input file. The rest of this page goes on about the implementation and the input file grammar.
The new exciting input file syntax is formally described in the schema. The schema is written in XML Schema, the language to describe XML grammar and data types.
An XML editor such as eclipse with xml plugins can use the schema for suggesting possible inputs in the current context.(Click to enlarge)
The possible attributes to an input element can be selected from a menu.
The Schema contains also documentation about the parameters and elements. This documentation can also be displayed in the XML editor.
The input reference lists all legal elements and attributes including definitions and explanation.