Preambles are descriptive text blocks that explain the purpose or meaning of a section, and the preferred model places them at the top of each section rather than only once at the top of the document. There's also a standard Introduction section, identical across all instances of a snapshot, that can serve a similar role. The reason STG values this explanatory layer so highly is that preserved records routinely outlive the original application and the people who knew how to read it — someone opening a record years after the source system is gone needs context, not just raw fields. Preamble content is configurable per section and is defined as part of the schema. It's the difference between a usable record and a pile of decontextualized data.