When only two files have been loaded into Merging, lines in each file are marked by glyphs to indicate when they differ from corresponding lines in the other file:
If two lines are identical, no glyph is displayed.
If two lines are different, a vertical bar (|) is displayed next to the line in each input text pane, and the different characters are highlighted.
If a line appears in one file but not in the other, a plus sign (+) is displayed next to the line in the file where it appears, and the different characters are highlighted.