<fn>

The <fn> element is a footnote used to annotate text with notes that are inappropriate for inline inclusion. It is also used to indicate the source for facts or other material used in the text.

Footnote content is skipped at the place where it was entered and rendered elsewhere, according to these rules:

A footnote with no specified @id attribute is a single-use footnote. Upon output, it generates a number as a superscript "callout" that is linked to the placement of the footnote, such as at the bottom of the immediate printed page or at the end of an online article. If a character is specified in the @callout attribute for the footnote, that character is used as the superscript "callout" that is linked to the placement of the footnote.
A footnote that specifies an @id attribute is a use-by-reference footnote. Upon output, it does not appear anywhere unless it has been referenced using an <xref> with the @type attribute set to "fn".
Ordinarily, a footnote in one topic can't be referenced in another topic. The previous behaviors are local to each topic. But by using the conref mechanism, you can create a new copy of another topic's footnote within the local topic where it will then follow these behaviors:
- If you use <fn conref="file.dita#topic/thatid"></fn> all by itself, the result will be the same as the single-use footnote entered literally in the same location. That is, it creates a local copy of the footnote with no local @id attribute, so it uses the behavior from the first bullet above.
- If you use <fn conref="file.dita#topic/thatid" id="thisid"></fn>, followed by <xref href="#thistopic/thisid" type="fn"/>, the result will be the same as the use-by-reference model described in the second bullet. That is, the <fn> element creates a local copy of the footnote with an id of "thisid"; that local copy is then referenced by the <xref> element.

The details of footnote processing and styling are implementation and/or stylesheet dependent. For example, a tool that renders DITA as PDF might lack support for the @callout attribute, or footnotes might be collected as endnotes for certain types of publications.

Content models

See appendix for information about this element in OASIS document type shells.

Inheritance

- topic/fn

Example

The first example is of a single-use footnote. It uses a simple <fn> element, with no @id and no @callout attribute. In that case, markup such as the following:

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.

might produce output similar to the following:

The memory storage capacity of the computer is 2 GB¹ with error correcting support.

......

¹ A GB (gigabyte) is equal to 1000 million bytes

----- [bottom of page] -----------------------------------------------------------------

The second example is a single-use footnote that uses a @callout attribute. It is marked up as follows:

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.

That DITA markup might produce output similar to the following:

The memory storage capacity of the computer is 2 GB^# with error correcting support.

......

^# A GB (gigabyte) is equal to 1000 million bytes

----- [bottom of page] -----------------------------------------------------------------

The third example is a use-by-reference footnote. It uses an @id on a footnote, and then references that @id multiple times. The DITA markup looks like this:

I like pets. <fn id="reuse-fn">This is the name of an animal.</fn>
At my house, I have a dog<xref href="#topic/reuse-fn" type="fn"/>, a
cat<xref href="#topic/reuse-fn" type="fn"/>, and a 
llama<xref href="#topic/reuse-fn" type="fn"/>.

and might produce output similar to the following:

I like pets. At my house, I have a dog¹, a cat¹, and a llama¹.

......

¹This is the name of an animal.

----- [bottom of page] -----------------------------------------------------------------

Attributes

The following attributes are available on this element: Universal attribute group, @outputclass, and the attribute defined below.

@callout: Specifies what character is used for the footnote link, for example a number or an alpha character. The attribute can also specify a short string of characters. When no @callout value is specified, footnotes are typically numbered.

@datatype: Available for describing the type of data contained in the value attribute for this metadata element. The default value is the empty string "".