"Sectioning" refers to organization of a document into separate sections, each with a title, some text, and possibly subsections. Each section is described in BoostBook via a <section> element. An introduction section may look like this:

<section id="any.intro">
  <title>Introduction</title>
 
  <para>Introduction to a library...</para>

  <section>
    <title>A Subsection</title>
    <para>Subsection information...</para>
  </section>
</section>

The <section> element contains all information that should logically be grouped within that section. The title of the section is placed within the <title> element, and any paragraphs, programs, lists, tables, or subsections can occur within the section. The id attribute of the <section> element gives a unique ID to each section, so that it may later be identified for linking. It is suggested that all IDs start with the short name of a library followed by a period, so that IDs do not conflict between libraries.