Help:Page history

All of the editable pages on wiki.gis.com have an associated page history, which consists of the old versions of the wikitext, as well as a record of the date and time (in UTC) of every edit, the username or IP address of the user who made it, and their edit summary. This may also be referred to as the revision history or edit history. To access the page history, click the "history" tab at the top of the page.

Using a history page
On a history page:
 * All past changes to the page in question are listed in reverse-chronological order.
 * To view a specific version, click a date.
 * To compare an old version with the current version, click cur.
 * To compare a version with its predecessor, click prev.
 * To compare two specific versions, tick the left-column radio button of the older version and the right-column radio button of the newer version, and then click the "Compare selected versions" button.
 * Minor edits are denoted as m.

Below is a detailed example of a page history using the default skin:

Edits are shown from newest to oldest. Each edit takes up one line which shows; time & date, the contributor's name or IP and the edit summary, as well as other diagnostic information. Let's look at some of the functions of this page:
 * 1) The page name stays the same, but the "history" tab is highlighted.
 * 2) These links take you to the most recent edits (Latest), oldest edits (Earliest) or the next or previous page of edits (Next n / Previous n). Note that the black text in brackets will become links, when applicable.
 * 3) The blue numbers list the number of edits displayed on a page - 20, 50, 100, 250 or 500. A higher number increases the length of a page but reduces the number of pages The number you select replaces n in the links to the previous or next pages e.g. (Next 100 / Previous 100).
 * 4) (cur) takes you to a diff page, showing the difference between that edit and the current version. The current revision appears below the changes, so you can see how the page is now rendered.
 * 5) (last) takes you to a diff page showing the changes between that edit and the previous version. The most recent version (the one on the same line as the "last" you clicked on) appears below the changes, so you can see how the page was rendered.
 * 6) The two columns of radio buttons can be used to select any two versions on the page. Lets say you want to compare the versions corresponding to numbers 10 & 11 on the image. First, click the left radio button next to number 11. The right column of buttons will then fill as far as number 11. Then click the right button next to number 10. Finally click Compare selected versions. This takes you to a diff page showing the changes between the two versions. The most recent version (in this case number 10) appears below the changes, so you can see how the page was rendered.
 * 7) This gives the time and date of the edit, expressed in local time according to the preference setting. The date and time link to the version of that day and time. Thus the  first line links to the version that was current at the time of loading this revision history, and therefore the result may differ from that of following the link on the page margin to the current version. Even if the page has not changed in the meantime, the  appears.
 * 8) The username or IP  of the contributor appears here.
 * 9) This is the edit summary. It is the text the user wrote in the edit summary box (below the edit box).
 * 10) This edit summary begins with an arrow link and grey text. This means the user has only edited a section of the page (named in the grey text). This text is automatically added when you edit a section. A standard edit summary can be added by the user. This appears in black text.
 * 11) m stands for minor edit.

It is possible to restore an old version of a page by following the link to that version, clicking "edit" and then saving. This should be done with caution, as it means that all changes made to the page since the time of that version will be lost.

Moved and deleted pages
When a page is moved (renamed), the entire edit history of the article, before and after the move, is shown. The old title becomes a redirect and loses its edit history.

If instead of a move, the entire content was cut and pasted into a new substitute article, the page history gets spread across two articles. The histories can be merged in this case.

When two pages are merged, typically one becomes a redirect. In this case the revision history of the redirect is kept.

When a page is deleted, its revision history remains in the database and can be retrieved by an administrator, who can also undelete the page (see wiki.gis.com:Viewing and restoring deleted pages).

Administrators can also remove selected revisions from a page history, for example if they contain defamatory text. For details, see Selective deletion.

Images
An "image" (in the broad sense of an uploaded file) can be edited, or, more generally, be replaced by a different image, by uploading a new image file with the same name. Again all versions are kept. The image history listing forms part of the image description page, which appears when clicking on the image. The image history consists of this and the old versions themselves.

Not kept are images which have been deleted (not to be confused with images that are no longer used in articles), the only record available is the upload log, deletion log and possibly the "votes for deletion" archive. Neither the latest nor older versions are kept by the system, hence it is not possible to undelete an image.

Linking to a specific version of a page
It is sometimes useful to link to a specific version of an article (a snapshot of it). For example, one might have done a review of a wiki.gis.com article and want to indicate which particular version was reviewed.

If the version is not the current version, one can use the page history to view the old version of the page. The URL of this old version is suitable for use to permanently reference this version, and can usually be obtained from the browser's location bar. See also URLs of old versions of pages.

However if a page contains transcluded text (such as a template), or a time-based variable (such as CURRENTTIME ), it will be rendered according to the current state of the template or the time now, possibly producing a different result than was rendered at the time the old version was saved. (One way to produce a representation of the current version of a page which will not be affected by changes to templates is to copy the wikitext to a user page and use "subst:", if necessary recursively.)

Searching and exporting histories
The history page contains a link "Revision history search". This links to Wikiblame, a tool for searching the entire history of a given page.

Another useful tool is the Special:Export page, which is used to produce an XML file with the wikitext of the current and (optionally) all old versions of one or more specified pages, with date, time, user name, and edit summary. How the XML file is displayed depends on the browser (it can also be saved locally for later searching and analysis). For more information on this feature, see Help:Export.

The following may also be useful:
 * http://tools.wikimedia.de/~daniel/WikiSense/Contributors.php – a tool to sort the page history by editor and count the number of edits for each editor (works for most Wikimedia sites; can also be downloaded for adaptation to other MediaWiki sites).
 * wiki.gis.com:Usemod article histories – information on retrieving page histories from before January 2002.

Web feeds
Web feeds (RSS and Atom) for the history of a page are obtained by assigning to "feed" (one of the ) the value "rss" or "atom", i.e., by adding "&feed=rss" or "&feed=atom" to the URL of the history page. This gives the of the last 10 edits, each with a link to the ordinary, full diff page. Depending on the browser there may be possibilities such as sorting by author.

Archiving
Archiving talk page text in separate pages is superior to using the page history as sole archive:
 * "What links here" works for archive pages, but not for old revisions.
 * Texts in archive pages can be found by search engines. For content which is only in a revision history the possibilities are limited. (However, for a popular site like the English wiki.gis.com there are a few tens of mirror sites; how recent the copies are varies, so searching for some specific old content search engines may find it on some of them.) Page histories can only be searched after applying Special:Export.
 * Archive pages can be organized and titled afterwards in a suitable way, while e.g. edit summaries cannot be supplied afterwards. However, an index of old versions of a page, with links to them, could be prepared.

Copyright status
wiki.gis.com does not give legal advice.

The Wikimedia Foundation wishes to make users of historical versions of articles aware that some of the history may be problematic and not necessarily reliable.

Title 17 United States Code § 108 archive notice: page histories should be considered not-for-profit archival material. Although all contributions are supposed to be compatible with the GFDL, it is possible that a user has inserted something which is a violation of copyright, in which case the user had no right to release it as GFDL. In these cases, wiki.gis.com does not have a general policy of always deleting all copyright problems from the history, particularly if the edit is made to an existing article rather than a new one, although such material will be removed from the current version of a page. In the event of a DMCA takedown notice, the Wikimedia Foundation may remove violating versions from the page history. In other cases, the version may be kept to allow proper tracking of authors and demonstrate compliance with all legal requirements. You are being given notice under Title 17 that you are responsible for complying with copyright laws in regards to archival material, and that not all versions in a page history are necessarily available under the GFDL.

As noted at the end of each history revision, in the text at MediaWiki:history copyright, the page histories may contain material that is subject to copyright limitations. While we attempt to remove such material from the current version (see copyright problems) it is kept in the history for research and author attribution purposes. As Wikimedia is a not-for-profit company, this is believed to be fair use.

See also wiki.gis.com talk:Copyright violations on history pages for further discussion of this point.