Use Case "SGML": Standard Generalized Markup Language
from XML Query Use Cases.

Source: http://www.w3.org/TR/xquery-use-cases/#sgml

Q1 - Locate all paragraphs in the report (all "para"
     elements occurring anywhere within the "report" element).
Q2 - Locate all paragraph elements in an introduction
     (all "para" elements directly contained within
     an "intro" element).
Q3 - Locate all paragraphs in the introduction of a
     section that is in a chapter that has no
     introduction (all "para" elements directly
     contained within an "intro" element directly
     contained in a "section" element directly
     contained in a "chapter" element.
     The "chapter" element must not directly
     contain an "intro" element).
Q4 - Locate the second paragraph in the third section
     in the second chapter (the second "para" element
     occurring in the third "section" element occurring
     in the second "chapter" element occurring in
     the "report").
Q5 - Locate all classified paragraphs (all "para"
     elements whose "security" attribute has the
     value "c").
Q6 - List the short titles of all sections (the
     values of the "shorttitle" attributes of
     all "section" elements, expressing each
     short title as the value of a new element.)
Q7 - Locate the initial letter of the initial
     paragraph of all introductions (the first
     character in the content [character content
     as well as element content] of the first
     "para" element contained in an "intro" element).
Q8a - Locate all sections with a title that has
      "is SGML" in it. The string may occur anywhere
      in the descendants of the title element,
      and markup boundaries are ignored.
Q8b - Same as (Q8a), but the string "is SGML" cannot
      be interrupted by sub-elements, and must
      appear in a single text node.
Q9  - Locate all the topics referenced by a
      cross-reference anywhere in the report
      (all the "topic" elements whose "topicid"
      attribute value is the same as an "xrefid"
      attribute value of any "xref" element).
Q10 - Locate the closest title preceding the
      cross-reference ("xref") element whose
      "xrefid" attribute is "top4" (the "title"
      element that would be touched last before
      this "xref" element when touching each
      element in document order).