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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.
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.

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.

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.

There are single-source publishing scenarios where a desired result can be achieved with either conditional processing or with transclusion (the conref feature).

For example, if a product name was going to vary between two choices from publication to publication, conditional processing with a product attribute could be used to exclude the inappropriate product name (to leave the appropriate product name). The code might look like: <ph product="Liberty">Liberty><ph product="Legend">Legend</ph>. When a ditaval rule of exclude elements with a product attribute of Liberty is applied, the remaining code would be <ph product="Legend">Legend</ph>.

The alternative approach would be to use transclusion, such as through a content reference (conref) to achieve the same result. The product name would not be included directly in the text; instead, a conref would be used to draw the phrase in from a separate conref file. The code might look like: <ph conref="conref_source/product_name" />. When a publication for the product with a name of Legend is required, the conref source file could be modified so that the conref source code was: <ph id="product_name">Legend</ph>.

The keyref feature introduced in DITA 1.2 makes this second transclusion method a lot easier and cleaner.

There are pros and cons with either approach.

The main advantages of the conditional processing method are:

all variations are visible to the author
a review version of the document can be produced that shows all variations

The main advantages of the transclusion method are:

topics are easier for an author to read
doesn't rely on metadata
easier to maintain if new variations are introduced (only the conref source file needs to be updated)
can cope better with large numbers of conditions