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Metadata, conditional processing, and indexing
Filtering and flagging
Content marked with metadata attributes can be conditionally processed so that the content is filtered (excluded) or flagged (highlighted) in the published output.
Excluding topics: conditional processing at topic level
If a whole topic is to be excluded from the output in a conditional processing scenario (that is, the condition applies to a whole topic), the metadata attribute must be defined in the topic reference in the ditamap.

Introduction
Information types and topics
Topics are the building blocks of modular documents, and organising topics by semantic information types is one of the architectural features of DITA.
DITA map files
Syntax and mark-up
Language and punctuation
Graphics and figures
Cross-referencing
Cross-references are a means of binding individual topics into a coherent and navigable document.
Content re-use
Metadata, conditional processing, and indexing
- Conditional processing concepts
  When DITA content is processed to a reading format, rules to exclude or highlight some of the content can be defined in a ditaval file. This conditional processing requires metadata attributes to be set on DITA elements that may possibly be excluded or highlighted.
- Condition (or select) attributes
  The audience, platform, product, otherprops and rev attributes can be applied to most DITA elements. They are used for conditional processing, and are known as the condition (or select) attributes.
- Filtering and flagging
  Content marked with metadata attributes can be conditionally processed so that the content is filtered (excluded) or flagged (highlighted) in the published output.
  - Excluding topics: conditional processing at topic level
    If a whole topic is to be excluded from the output in a conditional processing scenario (that is, the condition applies to a whole topic), the metadata attribute must be defined in the topic reference in the ditamap.
  - Conditional processing dangers
    Any filtering conditions that apply must still result in valid DITA mark-up.
  - Conditions versus transclusion
    Transclusion, or content referencing, can sometimes achieve the same publishing aim as conditional processing. There are pros and cons for either method.
  - Include and exclude filtering actions
    In typical publishing tools, filtering and flagging actions to be taken during processing are defined in a ditaval file.
  - Limiting the use of conditions
    You should take care to limit the complexity of conditions that you apply to content. Context-agnostic writing is often a better approach.
  - Filtering ditamaps
    When filtering a nested ditamap, you should apply the condition attribute to the reference (topicref or mapref element) to the nested ditamap, rather than to the map element.
  - Filtering composite (ditabase) topics
    Care must be taken when applying conditions to composite topics, as filtering a nested topic through the topicref element will not necessarily result in the topic being excluded.
  - Print versus non-print metadata
    You can use condition attributes in topic elements, the print attribute in the topicref element, separate ditamaps, or a combination of these approaches when you need to produce different print and non-print versions of the same document.
- Other metadata
  In addition to the select attributes, DITA content includes many forms of metadata. These metadata elements and attributes are used to manage and organise topics, ditamaps and publications.
- Indexing
  DITA incorporates powerful features for indexing, including multi-level indexing, and see and see-also redirection. Index entries can be applied in the ditamap, in the topic prolog, and inline within the topic content.
The DITA documentation process
DITA authoring concepts
Moving from style-based authoring to a structured authoring methodology such as DITA requires a radically different approach to writing.

Excluding topics: conditional processing at topic level

If a whole topic is to be excluded from the output in a conditional processing scenario (that is, the condition applies to a whole topic), the metadata attribute must be defined in the topic reference in the ditamap.

If you want to exclude a topic in a collection from the output, you have a number of options. These include:

Not including the topic in the ditamap, and processing a different ditamap when the topic is required.
Setting a condition attribute in the topic so that the topic can be filtered during the build process.
Setting a condition attribute in the topicref in the ditamap.

The best option is to construct different ditamap files for different publication outputs, rather than try to use the same ditamap with many condition attributes. The effort required to set up and maintain the condition attributes is a lot higher than working with different maps, particularly when the technique of using nested maps is used.

If having separate ditamaps is not practical, the best approach is to filter at the ditamap level (that is, apply the condition attribute value in the topicref element). If the topic is also referenced in the reltable section of the map, you must also apply the condition attribute to those topicref elements.

If a topic is to be excluded from an output based on conditions, logic suggests that the filtering condition attribute should be applied to the topic root element, and not to the topicref element (as recommended). For example, if the topic is intended for administrators only, then the condition metadata should be stored in the topic. However, excluding the entire content of a topic would leave an empty XML file; that is, an XML file without a root element. Such a file would be invalid, as an XML file must have a root element! The processing would then have to stop.

Applying a filtering attribute to the topicref element in the ditamap will only exclude the topic from the output if there is only the one reference to that topic. You should take care if applying conditions in the topic that you apply the conditions to all references to the topic, and that you do not leave dangling topicrefs.