* A colon, optionally followed by a stage number (0 to 3) and a
colon, followed by a path; this names a blob object in the
index at the given path. Missing stage number (and the colon
- that follows it) names an stage 0 entry.
+ that follows it) names an stage 0 entry. During a merge, stage
+ 1 is the common ancestor, stage 2 is the target branch's version
+ (typically the current branch), and stage 3 is the version from
+ the branch being merged.
Here is an illustration, by Jon Loeliger. Both node B and C are
a commit parents of commit node A. Parent commits are ordered