This is true for historical editions, literary editions, and editions which deal with the history of science, religion or any other discipline within the humanities. With this kind of markup, we begin to see how the document is organized. More striking, however, are the ways we can use the markup to infer information about the letter and other documents in the series. The more sophisticated SGML markup, in and of itself, describes only the structure of the letter. But basically, it's just a convenient way of saying one kind of data is being used to provide information about another kind data.
Scholarly editions have many kinds of metadata.
Printed volumes abound with footnotes or endnotes which provide additional information about the information contained in the documents. Editions frequently include biographical dictionaries which identify the characters of the cast. And they usually include indexes which provide conceptual views of the text. What makes these views and additions available in an electronic edition is the markup. One aim of the Partnership is to provide a range of prototypes which demonstrate some of the different ways of constructing intellectual views of the text.