As an API user, I would like to be able to access diffs between revisions of items (or properties, lexemes). Currently, the API only exposes the HTML rendition of these diffs, via the `compare` action:
https://www.wikidata.org/w/api.php?action=help&modules=compare
This returns HTML like this:
```
<tr><td colspan=\"2\" class=\"diff-lineno\">aliases / en / 0</td><td colspan=\"2\" class=\"diff-lineno\">aliases / en / 0</td></tr><tr><td colspan=\"2\"> </td><td class=\"diff-marker\">+</td><td class=\"diff-addedline\"><div><ins class=\"diffchange diffchange-inline\">PF3D7_0720400</ins></div></td></tr><tr><td colspan=\"2\" class=\"diff-lineno\">aliases / en / 1</td><td colspan=\"2\" class=\"diff-lineno\">aliases / en / 1</td></tr><tr><td class=\"diff-marker\">-</td><td class=\"diff-deletedline\"><div><del class=\"diffchange diffchange-inline\">PF07_0085</del></div></td></tr>\n<!-- diff cache key wikidatawiki:diff:wikidiff2:1.12:old-888082520:rev-888696170:1.7.3:25:lang-en -->\n
```
It would be great to have a JSON representation of these diffs as well. Currently, I can parse the HTML to extract the information I need, but this is brittle as any change in diff rendering could potentially break my consumer.
There is already a task T56328 about this in MediaWiki, but given that there is an even stronger case for this in Wikidata, I am creating a specific ticket for it. This could potentially be implemented by a dedicated API action given the different data format.
I do not have a particular JSON format to propose: anything that is easy to produce by the underlying PHP implementation would be great to have.