When you decide to focus on work on a specific article, you can add this template to ensure others won't edit it while you do.
Note however, if this template appear on an article for more than 4 days without changes to the article or removal of the template, any other user have the right to remove the template and continue work on the article. See the Working category for articles currently using this template.
Important: Usage has changed! Please notice how it works now.