What is in the bottom half of the 3-way merge

[JeanLibera]

When looking at a file that has already been merged, the BC3 window shows the following:

+--------------------------------------+
|            |            |            |
|   source   |   merged   |   source   |
|   file 1   |    file    |   file 2   |
|            |            |            |
+--------------------------------------+
|                                      |
|            WHAT IS HERE?             |
|                                      |
+--------------------------------------+

The question is, what is in the lower half of the window?
It seems to be a combination of source file 1 & source file 2,
but I can't figure out what it's purpose is, and why the
source lines here often differ from the merged file.

[Aaron]

Hello,

The center pane should be the "Ancestor" file, the oldest version of the file. The Left and Right are then Yours and Theirs (modifications common from the Ancestor file)
The bottom pane is then BC3 merging the 3 files together into a 4th output file.

Alternatively, you can launch a Text Merge with 2 top panes (Source1 and Source2) with a 3rd file as the bottom Output pane.

However, we do not load the file into the Output pane; the Output is always generated by the program from the top panes. Having a file here acts as the Save Target for the Output.

Does this help explain the setup of the 3 top panes and the 4th output pane?

[JeanLibera]

First, let me say that I am using Mercurial for version control. What you are describing, where the top middle pane has the ancestor, is true when I first use the BC3 to merge the file.

But after the file has been marked as are solved merge, meaning that I have already saved the merge results, then when I reopen the merged version of the file from hg tortoise, I get the BC3 merge window with the panes as described in my OP.

[Aaron]

How have you defined Mercurial to "re-open" the comparison? I suspect that would be a 3-way Compare, instead of 3-way Merge, but BC3 does not support a 3-way comparison. Our Text Merge session always requires the center pane be a common ancestor, and we do not have a session type for comparing the merged result file to two other files simultaneously.