There are tree levels of complaint in the IMS-LD specification:
Learning Design Level A includes everything described above except the conditions, properties and notifications. It thus contains all the core vocabulary needed to support dedagogical diversity.
Learning Design Level B adds Properties and Conditions to level A, which enable personalization and more elaborate sequencing and interactions based on learner porfolios. It can be used to direct the learning activities as well as record outcomes.
Learning Design Level C adds Notification to level B, which, although a fairly small addition to the specification, adds significantly to the capability.
There is a IMS Learning Design XML Binding document, where you can find detailed information about how each one of the elements described above is mapped in the final xml file.