When you specify a chunking attribute value, it overrides the default chunking behavior, which is to show each topic on its own page. For example, if you have a parent topic with several children, you can use the chunking attribute to specify if the topics appear on a single page or separate pages when publishing to HTML.

Here's an example map with some hierarchy:

When you publish this map with no chunking attribute applied, the parent topic shows on the page with links to each of the child topics. The following HTML example highlights this behavior.

When you publish this map with the to-content value for the chunking attribute, the parent topic and each of it's children show on the same page. The following PDF example highlights this behavior.

You can apply a chunk attribute to a single topic or to a map. When you apply a chunk attribute to a topic, the chunking behavior applies only to the topic and any children of that topic. When you apply a chunk attribute to a map, the chunking behavior is established for the entire map.

Here are the chunk attributes in DITA:

by-topic

Produces a separate output chunk for the target topic and each of its descendants.

by-document

Produces a single output chunk for the referenced document.

select-topic

Selects an individual topic.

select-document

Selects the topic and any other topics in the document.

select-branch

Selects an individual topic and any nested topics.

to-content

Generates a single document containing an individual topic and any nested topics.

to-navigation

Generates a new chunk of navigation, such as a Table of Contents.