Working With MediaWiki

was made (configured for the current user’s time zone), which link to a page showing that revision
the name of the user who made the edit, or the person’s IP address if the edit wasn’t made by a logged-in user
additional links to the user’s talk page and list of contributions
sometimes, the character “m” (in English), to indicate that the person who made this edit considered it a “minor edit”
the number of bytes in the page in this revision (for Roman letters, the number of bytes is usually equal to the number of characters, although for other languages, like Chinese, there are often three bytes per character)
the user’s own summary of the edit
an “undo” link, for all but the earliest row (covered in the upcoming section, “Undoing”).
    Clicking on the date/time brings you to the page for that specific revision — each one has its own permanent URL. Going to the URL for a specific edit shows you the contents of the page at that time, in addition to some information at the top about that revision:

    Administrators will also see links for “block” and “rollback” within the rows of the history page. These are both covered in the upcoming section, “Blocking and rollbacks”.

Page diffs
    The elements at the beginning of each row — “cur” and “prev” links (in English), and the two columns of radio buttons — are used to compare between revisions. Clicking on the “prev” link shows you the change made in this revision, while the “cur” link shows the differences between this revision and the current one. The sets of radio buttons, meanwhile, allow for precise comparison of any two revisions — the first column is meant to select an older revision, and the second column a newer revision (the JavaScript ensures that you can’t select a row in the second column older than the one in the first column). Clicking on “Compare selected revisions” will display all the differences between the two revisions.
    Figure 3.4 shows an example of one such display, from an edit made on November 21, 2011 to the article “Parallel postulate” on the English-language Wikipedia.
    Figure 3.4 A page diff from the English Wikipedia
    Colors and bolding are used to show differences. The algorithm used to determine the differences is MediaWiki’s own, and it’s fairly good, though not perfect. When one or more blocks of text are rearranged on the page, for example, the change is often shown as more dramatic than it actually is: it can be displayed as a massive deletion and addition of text, instead of a simple rearrangement.

Undoing
    The "undo" link, after the edit summary, allows any user to undo that one change. An "undo" link also appears in any page showing the difference between two revisions. Not every difference can be automatically undone, though, and thus not every "undo" link will work, whether it’s between a large number of revisions or just two adjacent ones. Clicking on an "undo" link that can’t be performed by the system will lead to the error message, "The edit could not be undone due to conflicting intermediate edits."
    MediaWiki decides whether or not a change can be undone based on whether the undo would affect any of the edits that have been done since the more recent of the two revisions. The more edits that have been done since the later revision, the smaller the chance that this change can be automatically undone. Conversely, a difference involving the current revision can always be automatically undone, whether it’s back to the previous revision or to any revision before that.
    If you can’t undo a change automatically, you’ll have to do it manually, which, for large pages, can be a painful process. In that case, using a text editor can usually make the task easier than editing the text directly within a web page.

Deleting revisions
    What if a person puts slanderous text, or reveals secret information, like someone’s phone number, on a wiki page? Of course, you can revert the edit, but that bad text will remain accessible to anyone who views the page history, and, if it’s a public wiki, it could even get linked to from elsewhere. That’s a bad outcome, but thankfully there’s a way for administrators to hide certain revisions altogether. In LocalSettings.php, you can add the following line:
$wgGroupPermissions['sysop']['deleterevision'] = true;
    This will give the ’deleterevision’ permission to all administrators. (We’ll get to user groups and