12.2. Model classes
A model class is a named group of elements that can be used in the same structural positions. Model classes do not appear in your XML as tags; you never write a model class in the document. Instead, they are part of the architecture behind the scenes.
You will most often encounter model classes when you are trying to understand a content model and you see something like ‘members of class X’. When that happens, you can look up the model class, read which elements belong to it, and return to the original element’s content model and interpret it as: ‘you may use one of these elements here’.
In practical terms, however, most lexicographers and encoders will not spend much time investigating or thinking about model classes. In day-to-day work, it is much more important for you to focus on individual elements, their attributes, and what other concrete elements are allowed within the given element. For instance, you cannot have a <def> within a <sense>, but you can have a <cit> within a <sense>, and within <cit>, you can have a <def>. Model classes make such rules possible, but they will be of more interest to super nerds who are maintaining Lex-0 or those who are interested in extending it or customizing it further.
