Types of DITA Comparison
At the topic level a detailed comparison between the two topics results in a new DITA topic. In the default mode of comparison the output format is set to DITA Markup, which highlights changes using DITA's rev or status attributes. There are also some XML editor specific 'track change' output formats, as discussed in Output Formats.
A Mapfile Comparison is a 'flat' comparison of two DITA map files. No ditamap references to sub-maps are followed and any topics referenced are not compared. The result therefore provides information about changes to the map files alone.
Map Topicset Comparison
This comparison begins at the map level. The comparator aligns the topics between the maps, compares the aligned topic, and returns a map, or maps, that contain the compared, added, and deleted topics. Each topicref in the output map has a status attribute set to one of unchanged, changed, deleted, or new, depending on whether the underpinning topic (i.e. the referent) has no reportable modifications, has some reportable modification, has been inserted, or has been deleted respectively. Here, a reportable modification is one that can be marked up in the chosen output format's change markup scheme.
Setting an Output Format for a Map Topicset Comparison only affects markup in the referenced topics, the markup within the map files is always in the form described above.
The content of a DITA Map file is not compared. Instead, a DITA map is used to specify a collection of topics that are of interest. And it is these topics that are compared. The results of the topic comparisons are then used to modify existing maps and/or create new maps.