Restricts the generic skill type by specifying the data type of the elements that describe the level of knowledge of the language and related linguistic diplomas and/or experiences. Defines a Linguistic Certificate by restricting the allowed type for the level element to be "CEFLanguageLevel" Extends the generic ExperienceType to include information about an experience that results in acquiring linguistic skills. Contains information about the period the linguistic experience took place and the area/context into which it is acquiared. Defines a list of Experiences.