Blacklining or Redlining?

In short: Blacklining is for understanding document differences between completed versions. Redlining is for collaboratively developing document drafts.

Let's look at the difference and also understand the role of "Track Changes":

1. Blacklining

Typical applications for blacklining include:

• Confirming that there are no changes between two document versions.
• Documenting the change history between an old and a new version.

Blacklining simply involves comparing two documents and is done using a so-called two-way diff.

Unless your software system provides features to collaborate on and store document drafts, blacklining may be all you need for change highlighting.

2. Redlining

Redlining means identifying the differences between document draft versions while multiple parties edit them.

To review a draft with changes made by you and others, you need to identify differences as well as attribution, indicating who is responsible for each change.

There are two approaches to implementing redlining:

a) Track Changes

Track Changes highlights edits as they occur, with attribution added by storing the author of each edit. While commonly used, Track Changes has known flaws:

• It often generates cluttered redlines (compare its performance against TreeDiff here).
• It requires everyone to edit the same shared document.
• Multiple authors cannot make conflicting edits, as there is no "alternative redlines", hindering negotiation.

b) Three-way diff

This approach involves calculating a three-way diff between the two documents and the shared base document that both parties edited (What is a Three-way Diff?).

• A sophisticated comparison algorithm like TreeDiff significantly improves redline readability, as shown in our tools comparison.
• It allows unrestricted document edits.
• There's no need to adhere to Track Changes settings or "redlining etiquette" (examples
  here
  and
  here
  ).

In Summary

Blacklining involves a comparison between two documents to highlight differences.

Redlining uses a Three-way Diff or Track Changes to attribute differences to authors.

A sophisticated Three-way Diff like TreeDiff surpasses Track Changes in readability.