The format attribute identifies the format of the resource that is referenced. If no value is specified, but the attribute is specified on an ancestor within a map or within the related-links section, the value will cascade from the closest ancestor.
The following values for format have special processing implications:
- The destination uses DITA topic markup or markup specialized from a DITA topic. Unless otherwise specified, when format is set to "dita", the value for the type attribute will be treated as "topic".
- The linked-to resource is a DITA map. It represents the referenced
hierarchy at the current point in the referencing map.
References to other maps can occur at any point in a map, but
because relationship tables are only valid as children of a map,
referenced relationship tables are treated as children of the
referencing map. Note: If a topicref element that references a map contains child topicref elements, the processing behavior regarding the child topicref elements is undefined.
- (no value)
- The processing default is used. The
processing default for the format attribute is
determined by inspecting the value of the href
attribute. If the href attribute specifies a
file extension, the processing default for the
format attribute is that extension, after
conversion to lower-case and with no leading period. The only
exception to this is if the extension is "xml", in which case
the default format is "dita". If there is no extension, but the
href value is an absolute URI whose
scheme is "http" or "https", then the processing default is
"html". In all other cases where no extension is available, the
processing default is "dita".
If the actual format of the referenced content differs from the effective value of the format attribute, and a processor is capable of identifying such cases, it MAY recover gracefully and treat the content as its actual format, but SHOULD also issue a message.
For other formats, using the file extension without the "." character typically represents the format. For example, the following values are all possible values for format:
- The format of the linked-to resource is HTML or XHTML.
- The format of the linked-to resource is PDF.
- The format of the linked-to resource is a text file.