Three Input Files

When an ancestor file has been specified for the two files to be merge, lines in each descendant are marked according to their relationship to the corresponding lines in the common ancestor:

• If a line is identical in all three files, no glyph is displayed.

• If a line is not in the ancestor but was added to one or both of the descendants, a plus sign (+) is displayed next to the line in the file where the line was added, and the different characters are highlighted.

• If a line is present in the ancestor but was removed from one or both of the descendants, a minus sign (-) is displayed next to the line in the file from which the line was removed, and the different characters are highlighted and in strikethrough.

• If a line is in the ancestor but has been changed in one or both of the descendants, a vertical bar (|) is displayed next to the line in the file where the line was changed, and the different characters are highlighted.

Resolved differences are marked by glyphs in outline font.

Table 4-1 summarizes the automerging algorithm. Ancestor is the version of a text line that is in the ancestor file; Change 1 is a change to that line in one of the descendants; Change 2 is another change, different from Change 1. Only when a line is changed differently in the left and right descendants does automerging fail.

Table 4-1 Automerging Rules Summary

Left Descendant	Right Descendant	Automerged Line
Ancestor	Ancestor	Ancestor
Change 1	Ancestor	Change 1
Ancestor	Change 2	Change 2
Change 1	Change 1	Change 1
Change 1	Change 2	No Automerge

When Merging automatically resolves a difference, it changes the glyphs to outline font. Merging lets you examine automatically resolved differences to be sure that it has made the correct choices.

You can disable automatic merging by deselecting Auto Merge on the Options menu. When automatic merging is disabled, Merging constructs a merged file using only lines that are identical in all three files and relies on you to resolve the differences.

If you do not specify an ancestor file, Merging has no reference with which to compare a difference between the two input files. Consequently, Merging cannot determine which line in a difference is likely to represent the desired change. The result of an automerge with no ancestor is the same as disabling automatic merging: Merging constructs a merged file using only lines that are identical in both input files and relies on you to resolve differences.