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Syntax and mark-up
Procedures and steps
The purpose of procedural documents is to explain to the reader how to accomplish tasks. The task information type is specifically designed for procedures, with a well-defined structure built around steps.
The prereq element
The pre-requisites (prereq) element describes the status or situation that must be established before a procedural task can be started. It can contain cross-references to pre-requisite task topics.

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
- Organisation of DITA elements
  Elements in DITA are grouped together into a number of categories for organisational and comprehension purposes.
- Working with mark-up
- Element domains
  Elements in DITA are arranged into domains for organisational purposes and technical reasons.
- Short descriptions
  The short description (or shortdesc) is arguably the most important component of a DITA topic, and is also one of the most difficult elements to write. Short descriptions should be written for every topic.
- Lists
  The purpose of a list is to make it easier for the reader to understand sequences of information and collections of like information. Different types of lists are used for different information structures.
- Paragraphs
  Paragraphs are the basic components of topics. A paragraph (p) element should be a self-contained unit dealing with one idea or point, typically expressed in two or more related sentences. The p element should be used when no other semantically-specific block element is available.
- Procedures and steps
  The purpose of procedural documents is to explain to the reader how to accomplish tasks. The task information type is specifically designed for procedures, with a well-defined structure built around steps.
  - Semantics in steps
    The steps of a procedure are defined in a task topic. Task topics typically have a simple structure of a single set of steps, but some procedures may require a more sophisticated structure that includes substeps and decision points.
  - Separating procedures into granular steps
    Steps within a task topic must be written so that a single step contains just one user action (known in DITA as a command).
  - Restricting tasks to one procedure only
    Task topics can only contain one procedure, with one continuous set of numbered steps.
  - The prereq element
    The pre-requisites (prereq) element describes the status or situation that must be established before a procedural task can be started. It can contain cross-references to pre-requisite task topics.
  - Substeps within steps
    Task topics allow two levels of steps within a single procedure: steps and substeps. Where possible, substeps should be avoided.
  - Single step procedure
    A procedure or task containing just one action should be marked-up using the normal steps/step/cmd structure.
  - The command element
    The command (cmd) element within the step element contains a single, active voice instruction to the reader.
  - Required and optional steps
    The importance attribute of a step is used to indicate whether an element is optional or mandatory.
  - Complex nested tasks
    A complex process made up of a number of procedures can be documented by collecting, through the ditamap, the constituent task topics under a process stub topic.
  - Notes and extra information in a step
    Information that supplements or supports a procedural step can be included within an info element. The info element in turn can contain block elements such as note elements.
  - Images within steps
    Images that support a procedural step can be included within a stepxmp or an info element.
  - Choice tables
    A choice table is used within a step in a task topic to describe a series of optional choices that a user must make before proceeding.
  - Non-sequential procedural steps
    Some procedures are not made up of sequential procedural steps. When documenting these procedures, the steps-informal structure or the steps-unordered structure should be used.
- Tables
  The purpose of a table is to structure, organise and present factual data that a user will need to look up or reference. There are two general purpose table types in DITA: table and simpletable.
- Phrases
  The semantics of words and phrases in DITA content is expressed through a broad range of phrase elements.
- Special characters and dates
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
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.

The prereq element

The pre-requisites (prereq) element describes the status or situation that must be established before a procedural task can be started. It can contain cross-references to pre-requisite task topics.

The optional pre-requisites (prereq) element in task topics is used to describe the things that a user needs to know or do before starting the task.

During output to a reading format, the pre-requisite (prereq) element should be labelled so that the reader can identify the information as being a pre-requisite state.

The prereq element must read as one or more complete sentences.

Normally you should only need to have one block of pre-requisite information, and you should not nest a single, redundant paragraph (p) element within the prereq element. However, if you need to include more than one block, you will need to nest paragraphs inside the prereq element.

For example, a typical single-block pre-requisite should be structured as:

<prereq>Ensure...</prereq>

while a lengthy pre-requisite with more than one block should be structured as:

<prereq>
  <p>Ensure...</p>
  <p>Prepare...</p>
</prereq>

If there are any topics that document pre-requisite tasks, these should be added as links in the related-links section at the bottom of the topic, with the link element's importance attribute set to required. This will result in those links being placed under the pre-requisites block during processing to a reading format.

The following example shows a typical presentation of a required link from the related-links section in a task topic processed to XHTML.

Screen capture showing XHTML output of required related-links in Pre-requisites section — Figure 1. Typical XHTML output of related-links with importance setting of required