In some organizations, Sitecore CMS users function as both editors and reviewers in a single workflow, but should not be able to review and approve their own changes. There is no “out-of-the-box” Sitecore feature that meets this requirement, but it’s relatively easy to add one.

Add a class such as the following to the Visual Studio project:

namespace Sitecore.Sharedsource.Workflow.Actions
{
  using System;

  public class ValidateApprover
  {
    public void Process(Sitecore.Workflows.Simple.WorkflowPipelineArgs args)
    {
      if (String.Compare(
        args.DataItem.Statistics.UpdatedBy,
        Sitecore.Context.User.Name,
        true) != 0)
      {
        return;
      }

      Sitecore.Web.UI.Sheer.SheerResponse.Alert(
        "You cannot approve your own changes.");
      args.AbortPipeline();
    }
  }
}

In the Content Editor, under the Approve command under the Review state of the workflow, insert an item named ValidateApprover using the System/Workflow/Action data template. In the Data section, in the Type string field, enter the type signature:

Sitecore.Sharedsource.Workflow.Actions.ValidateApprover, Assembly

I added this class to the Sitecore Shared Source Library project and updated the corresponding documentation.