Each Comparison Pane contains margin indicators that provide visual cues to certain actions during the editing of your code. The margin indicators appear in the Margin Bar on left side of the pane:
Bookmark - A marker used to locate lines in a source file.
Visual Comparer allows establishing bookmark on every line in the Comparison Pane. It allows speeding up navigation on a file in case of its large size. How to set up, remove and move on bookmarks, see please menu Edit.
Edited line - A marker used to indicate that this line has been edited during of comparison of the files.
Virtual line - A marker used to indicate that this line is virtual line.