The format attribute

Darwin Information Typing Architecture (DITA) Version 1.2

The format attribute identifies the format of the resource being cross referenced. The processing default for format is "dita". 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.

Using the format attribute

Possible values for this attribute include:

dita
The destination uses DITA topic markup or markup specialized from a DITA topic. Unless otherwise specified, the corresponding default type will be treated as "topic."
html
The format of the linked-to resource is HTML or XHTML.
pdf
The format of the linked-to resource is PDF (opens a new window).
ditamap
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 may 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.
(no value)
Processors default to "dita"

For other formats, you can use the file extension without the "." (for example, in a link to file "readme.txt", use "txt" as the value).