The topic structure has the following major parts: • is the container for a single unit of typed information. Tightly-related topics may be nested for reuse as a single construct. • provides self-description, consistent with guidelines for authoring. • provides optional title content optimized for search or for navigation. • provides an abtract-level description of the content of the topic. Shortdesc is optional at the topic level for generality when specializing. For User Assistance, the best practice is to use shortdesc as if it were a required first or only paragraph. • contains optional metadata, or information about the document or its content. • is the container for paragraph-level content and any number of non-nesting sections. • is an optional container for in-topic link relations. Links can also be maintained separately from topics by using a DITA map to express the linking relationships between topics. •