What are card revisions?
The card revisions functionality saves a new card revision every time a card is updated. This is useful for value changes that are recorded as a historical event but the old value is not always preserved in the History tab. Most commonly, this feature is used to see how and when the card's description has changed.
It allows for every given change in a card to be recorded and provides the ability to restore the previous state. This provides a safety net when multiple people work on a card at the same time, or simply a way to track the progress on a given card through the revisions.
Where to access the card revisions from?
In order to access a card’s revisions, a user must have a board role that allows them to open the card details and edit them.
You can find each card's revisions in the three-dot menu in the top right corner.
How to restore a card to a previous revision?
When you click on the rescission button, a list of all the Card Versions. After selecting the version you want to look at the following window will appear that details the properties of that card in the selected version.
You can either restore all the card fields to the version or you can deselect irrelevant ones.
Note: the card attachments, watchers, and position cannot be restored to a previous revision. Custom fields will be merged.
When deleting a subtask, a new revision is created.
When deleting multiple subtasks, multiple revisions are created, so check carefully whenever you restore a card to a previous revision.
Because card revisions are made to take the current version of the card and compare it to the previous revision, there are cases where you can restore more than the intended subtasks.
For example, you have a card with 4 subtasks, A, B, C, D.
If you delete subtask D, a revision will be created. And on your current card, you will have subtasks A, B and C.
If you then delete subtask C, another revision will be created. And on you current card you will have subtasks A and B.
Now when you go back and try to restore the revision with subtask D, you will restore both subtask C and D because the difference between the revision and the current card are both of the subtasks.
You can then delete subtask C so you can have the desired result of just having subtasks A, B and D on the card.