The XmlChan class allows AST objects to be represented in the form of XML in several ways (conventions) and the XmlFormat attribute is used to specify which of these should be used. The formatting options available are outlined in the "Formats Available" section below.
By default, an XmlChan will attempt to determine which format system is already in use, and will set the default XmlFormat value accordingly (so that subsequent I/O operations adopt the same conventions). It does this by looking for certain critical items which only occur in particular formats. For details of how this works, see the "Choice of Default Format" section below. If you wish to ensure that a particular format system is used, independently of any XML already read, you should set an explicit XmlFormat value yourself.
The following points should be noted when using an XmlChan to read or write STC information (note, this list is currently incomplete):
AST A Library for Handling World Coordinate Systems in Astronomy