An empty element that identifies an instance of the <Audience> composite as representing the primary or main audience for the product. The main audience may be expressed in more than one audience scheme, ie there may be two or more instances of the <Audience> composite, using different schemes, each carrying the <MainAudience/> flag, so long as there is only one main audience per scheme (ie per value of <AudienceCodeType>). Optional and non-repeating in each occurrence of the <Audience> composite.