The Professional Edition of Merge enables you to compare three folder hierarchies side-by-side.
To switch between two-way and three-way comparisons select Two-Way Vertical or Three-Way Vertical from the Layout toolbar button. You can also select Window▸Two-way Vertical and Window▸Three-way Vertical, or press Ctrl+Cmd+2 and Ctrl+Cmd+3.
Ordering of compared folder hierarchies in the comparison display
When you compare three folders, Merge assumes that the central folder is the common ancestor of the folders to the left and right. This means that launched three-way file comparisons will be opened with the common ancestor of each file in the centre panel. This is important to effective operation of file comparisons. The ordering of the folder hierarchies also affects the colouring that Merge will apply to files and folders to indicate their state.
Understanding the display
Files that are only present in the common ancestor hierarchy are considered removed. Files that are present in either of the other hierarchies, but not in the common ancestor, are considered inserted.
Files and folders are shown in the folder comparison display with a background colour appropriate for their state (removed, inserted, unchanged or changed). The colours are those configured on the Fonts/Colours preferences page.
For three-way folder comparisons, the third Changes column indicates the number of changes between the first and third folder hierarchies.
Launching file comparisons
When you launch file comparisons from a three-way folder comparison, a three-way file comparison window is opened if the row being compared contains three files. If only two files are present in the row, a two-way file comparison window is opened.
Visibility filters that you set using the Visibility Filters… menu item in the Hide Reveal toolbar button or Actions▸Hide/Reveal menu, for two and three-way comparisons, operate independently. You can view and modify the filters that are in force for two and three-way comparisons at any time by using the controls in the Filters page of the preferences dialog.