Hiding individual lines from a page history or log is possible due to the RevisionDelete functionality added to the MediaWiki core codebase (i.e., from Mediawiki Version 1.16) in mid-2009. (See section Pre-1.16 Hacks below to accomplish similar tasks on older versions of MediaWiki.) The revision deletion feature is available to users in at least one usergroup that has been given the deleterevision permission (which is not assigned to any group by default) in the MediaWiki configuration. The function has the ability to show/hide the revision itself, the name of the user who made the edit, or the edit summary used - or any combination of those three.
When enabled on an installation and viewed by a user with the appropriate permissions, every page revision and log entry has a smallbutton displayed next to it, as shown in the normal revision and protection log entry below.
- (cur) (prev) 00:00, 1 Jan 1970 WikiUser (X bytes) (Edit summary) (undo)
- WikiUser protected "Page" [edit=sysop] (indefinite) [move=sysop] (indefinite) (Log summary) 00:00, 1 Jan 1970
When a revision or log entry is hidden from view in its entirety, it is displayed like that shown below, with the elements hidden from view stricken and greyed out. Once a revision is hidden, the contents of the revision (if hidden), cannot be viewed by any usergroup without the deleterevision right. Trying to compare the revision with other revisions or access its &oldid= page will result in an error stating that the revision has been removed from the public archives. Similarly, trying to search for a hidden log entry by the users involved, when they have been hidden, will turn up no results.
- (cur) (prev) 00:00, 1 Jan 1970 (username removed) (comment removed) [deleted]
- (username removed) (log action removed) (comment removed) 00:00, 1 Jan 1970
NOTE: Revision deletion remains applied to a page even when deleted. If a page is undeleted, revisions that were previously hidden with RevisionDelete will remain hidden to the public.
Using RevisionDelete 
Hiding a revision 
To show/hide a revision, click the smallbutton next to the relevant revision or log entry that you wish to show/hide. Depending on your permissions, there may be between 3 and 4 different options to choose from:
- show/hide revision text
- show/hide edit comment
- show/hide editor's username/IP
- Apply these restrictions to Sysops and lock this interface (only available to users with the suppressrevision right)
Tick the checkboxes next to each of the items that you wish to apply to the selected and then provide an informative summary in the "Log comment field". Once this information has been filled in, click the "Apply to selected revision" button to submit the information. If this has been done correctly, Revision visibility successfully set should be displayed on your screen.
Unhiding a revision 
To show/unhide a revision, click the Revision visibility successfully set message.button for the revision or log entry and simply untick all the boxes, provide your summary and click the "Apply to the selected revision" button. Success should be marked by the display of the
Changing the visibility settings 
This is quite similar to unhiding a revision; click thebutton and tick/untick the options that you wish to modify and click the apply button.
Pre-1.16 Hacks 
If you are on a pre-1.16 Mediawiki installation, this core feature is unavailable. However, sysops may (destructively) accomplish selective deletion of revisions by first deleting a page and then selectively restoring its revision. This will, however, permanently delete all revisions not restored in the process, unless a number of moves is included in the process to the effect that the revisions not restored remain in a page that will be otherwise redundant at its end. That is (NO GUARANTEES!): 1. move "ARTICLE" to "ARTICLE (damaged)" 2. delete the latter, 3. selectively restore the latter, 4. move the latter to its original title. 5. delete (!) the redirect left over by the last move, 6. voilà, the revisions not restored may be still there under "ARTICLE (damaged)" (which consists of the deleted revisions not restored). Be sure to keep that deleted unless you want nosey users to read these revisions. Page protection (sysop only) on the deleted page may be required to keep users from recreating the page which might potentially destroy the old revisions.
Log entries 
Normally, hiding a revision or page history item will produce a log message in the public deletion log or the private supression log (if "Apply these restrictions to Sysops and lock this interface" is ticked). Log entries created in the public deletion log look like those displayed below for page revision and log entries visibilities respectively.
- WikiUser changed revision visibility of Page (hid content, edit summary, username for 1 revision: Log summary) 00:00, 1 Jan 1970
- WikiUser changed event visibility of (Protection log) (hid content, edit summary, username for 1 event: Log summary) 00:00, 1 Jan 1970
Thelink displayed leads to the visibility settings for that particular log entry, while the button leads to the visibility settings for the page affected by that particular log entry.
See also