Reference Validation in DITA Documents

Serna helps you keep all references valid:

Validation in DITA dialogs
Using DITA dialogs ensures you make valid references:
- In a DITA dialog, you select the target from the offered list of available targets.
- If you are entering a path manually in a DITA dialog, it is validated. In the case of typing an invalid link, the Files list, Targets list, File type filter and Show types filter get disabled.
  
  Figure 1. Invalid path in the Insert External Xref dialog. Widgets are disabled.
Validation by the stylesheet
Stylesheets validate existing references. Your document may contain invalid references in the following cases:
- A document was previously authored outside of Serna.
- A reference was edited through the Attributes dialog when validation mode wasn't Strict.
If there is an inaccessible path, the broken reference is shown in red.

Figure 2. Invalid path is validated by the stylesheet.
Validation by the Schema
Serna reports invalid local references in the following cases:
1. When you try to insert an invalid local reference
  When you try to insert an invalid local reference through the Attributes dialog, Serna behaves the following ways depending on the current validation mode:
  - Strict Validation
    
    The error message appears and the operation is cancelled.
    
    Figure 3. Message: Operation not valid in context.
  - Validation On
    
    The invalid reference is inserted but a message reporting the not found target appears. You should correct the reference.
    
    Figure 4. Serna reports an invalid local reference.
  - Validation Off
    
    The invalid reference is inserted without any messages.
2. When you open a document with invalid local references
  Your document may contain invalid references in the following cases:
  - A document was previously authored outside of Serna.
  - A reference was edited through the Attributes dialog when validation mode wasn't Strict.
  If there is an inaccessible path to a target within the current document, validation mode switches from Strict to On, and, in addition to the broken local reference in red, a message reporting the not found target appears.
  
  Figure 5. Serna reports an invalid local reference.