<fn>

A footnote is ancillary information that typically is rendered in the footer of a page or at the end of an online article. Such content is usually inappropriate for inline inclusion.

Usage information

There are two types of footnotes: single-use footnote and use-by-reference footnote.

Single-use footnote
This is produced by a <fn> element that does not specify a value for the @id attribute.
Use-by-reference footnote
This is produced by a <fn> element that specifies a value for the @id attribute. It must be used in conjunction with an <xref> element with @type set to fn.

To reference a footnote that is located in another topic, the conref or conkeyref mechanism is used.

Rendering expectations

The two footnote types typically produce different types of output:

Single-use footnote
When rendered, a superscript symbol (numeral or character) is produced at the location of the <fn> element. The superscript symbol is hyperlinked to the content of the footnote, which is placed at the bottom of a PDF page or the end of an online article. The superscript symbol can be specified by the value of the @callout attribute. When no @callout value is specified, footnotes are typically numbered.
Use-by-reference footnote
Nothing is rendered at the location of the <fn> element. The content of a use-by-reference footnote is only rendered when it is referenced by an <xref> with the @type attribute set to fn. If an <xref> with the @type attribute set to fn is present, a superscript symbol is rendered at the location of the <xref> element. Unless conref or conkeyref is used, the <fn> and <xref> must be located in the same topic.

However, the details of footnote processing and formatting are implementation dependent. For example, a tool that renders DITA as PDF might lack support for the @callout attribute, or footnotes might be collected as end notes for certain types of publications.

Attributes

The following attributes are available on this element: universal attributes and the attribute defined below.

@callout
Specifies the character or character string that is used for the footnote link.

Examples

This section contains examples of how the <fn> element can be used.

Figure 1. An example of a single-use footnote

The following code sample shows a single-use footnote. It contains a simple <fn> element, with no @id or @callout attribute.

<p>The memory storage capacity of the computer is 2 GB
<fn>A GB (gigabyte) is equal to 1000 million bytes</fn> 
with error correcting support.</p>

When rendered, typically a superscript symbol is placed at the location of the <fn> element; this superscript symbol is hyperlinked to the content of the <fn>, which is typically placed at the bottom of a PDF page or the end of an online article. The type of symbol used is implementation specific.

The above code sample might produce the following output similar to the following:


The screen capture shows a text in a document that includes a footnote. In the body of the text, the location of the footnote is marked with the numeral one in superscript. At the bottom on the page, the text of the footnote appears along with the associated numeral one. The edges of the screen capture are tattered, to indicate that the image is part of a larger document.
Figure 2. An example of a single-use footnote with a @callout attribute

The following code sample shows a single-use footnote that uses a @callout attribute:

<p>The memory storage capacity of the computer is 2 GB
<fn callout="#">A GB (gigabyte) is equal to 1000 million bytes</fn>
with error correcting support.</p>

The rendered output is similar to that of the previous example, although processors that support it will render the footnote symbol as # (hashtag).

Figure 3. A use-by-reference footnote

The following code sample shows use-by-reference footnotes. The <fn> elements have @id attributes, and inline <xref> elements reference those <fn> elements:

<section>
  <fn id="dog-name">Fido</fn>
  <fn id="cat-name">Puss</fn>
  <fn id="llama-name">My llama</fn>
  <!-- ... -->
  <p>I like pets. At my house, I have 
     a dog<xref href="#topic/dog-name" type="fn"/>,
     a cat<xref href="#topic/cat-name" type="fn"/>, and
     a llama<xref href="#topic/llama-name" type="fn"/>.
  </p>
</section>

The code sample might produce output similar to the following:



Figure 4. A single-use footnote that uses conref

The following code sample shows footnotes stored in a shared topic (footnotes.dita):

<!-- Content from footnotes.dita -->
<topic id="footnotes">
  <title>Shared topic...</title>
  <body>
    <bodydiv>
      <fn id="strunk">Elements of Style</fn>
      <fn id="DQTI">Developing Quality Technical Information, 2nd edition</fn>
      <!-- ... -->
    </bodydiv>
  </body>
</topic>

To use those footnotes, authors conref them into the relevant topics:

<p>See the online resource<fn conref="footnotes.dita#footnotes/DQTI"/> for more 
   information about how to assess the quality of technical documentation ...</p>
Figure 5. A use-by-reference footnote that uses conref

The following code sample shows a use-by-reference footnote that uses conref:

<topic id="evaluating-quality">
  <title>Evaluating documentation quality</title>
  <body>
    <bodydiv>
      <fn conref="footnotes.dita#footnotes/DQTI" id="dqti"/>
    </bodydiv>
    <!-- ... -->
    <p>See the online resource<xref="#./dqti" type="fn"/> for more 
       information about how to assess the quality of technical documentation./p>
    <!-- ... -->
  </body>
<topic>