One of the features we're planning to implement in the new HMRC manuals is the ability for people to see the manuals at a specific date in the past.
Whilst this is useful in itself, ultimately we want to make it easy for people to see specifically what's changed between two versions of a particular manual. Feedback from a recent user testing session confirmed that this would indeed be a useful feature.
I implemented a similar feature on the whitehall publishing system for GOV.UK which produces a view for editors see the differences between two versions and comment on the changes, below is an example of the output:
The code which powers this feature is the google diff-match-patch library, one of the many benefits of this library is that you can see the changes inline and customise the way the output is displayed to match your needs.
This style of output is useful for editors as it's similar to MSWord track changes, however for the manuals web interface we are planning to change it to look like the this:
We'll continue to develop this idea based on user feedback so let us know what you think.