The window is accessible by the command 'Diff version' from IDE. It allows comparing of the current version of a file with one of the versions in the repository. The necessary version can be chosen in the field "with version", and the required comparison program - in 'Diff tool selection'. By default the last version in the repository (HEAD) is selected for comparison. Besides, comparison with BASE version is possible - the version before performing checkout operation. Or with the local BASE version, which has been saved locally before checking out. The comparison with this version is available even offline. Choose 'Display only if shift key is down' to hide this window.