A model description consists of several parts, each of which starts with a descriptor, such as STATECHART and TRANSITION. A model may specify the same descriptor many times.
In the text file of a model description, a descriptor is a single line with an ending colon ``:''. All the following lines pertain to that descriptor until a new descriptor appears. Empty lines are lines that contain only spaces, tabs and/or comments (see below). Empty lines are automatically ignored.
Descriptor STATECHART is necessary for every model, which defines the state hierarchy. As least one default state must be defined for the hierarchy. Other descriptors are optional.