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Visual editing Wikis can also make WYSIWYG editing available to users, usually through a JavaScript control that translates graphically entered formatting instructions into the corresponding HTML tags or wikitext. In those implementations, the markup of a newly edited, marked-up version of the page is generated and submitted to the server transparently, shielding the user from this technical detail. An example of this is the VisualEditor on Wikipedia. WYSIWYG controls do not, however, always provide all the features available in wikitext, and some users prefer not to use a WYSIWYG editor. Hence, many of these sites offer some means to edit the wikitext directly. Version history Some wikis keep a record of changes made to wiki pages; often, every version of the page is stored. This means that authors can revert to an older version of the page should it be necessary because a mistake has been made, such as the content accidentally being deleted or the page has been vandalized to include offensive or malicious text or other inappropriate content. Edit summary "Edit summary" redirects here. For the Wikipedia help page, see Help:Edit summary. Many wiki implementations, such as MediaWiki, the software that powers Wikipedia, allow users to supply an edit summary when they edit a page. This is a short piece of text summarizing the changes they have made (e.g. "Corrected grammar," or "Fixed formatting in table."). It is not inserted into the articlecommas main text but is stored along with that revision of the page, allowing users to explain what has been done and why. This is similar to a log message when making changes in a revision-control system. This enables other users to see which changes have been made by whom and why, often in a list of summaries, dates and other short, relevant content, a list which is called a "log" or "history." Navigation Within the text of most pages, there are usually many hypertext links to other pages within the wiki. This form of non-linear navigation is more "native" to a wiki than structured/formalized navigation schemes. Users can also create any number of index or table-of-contents pages, with hierarchical categorization or whatever form of organization they like. These may be challenging to maintain "by hand", as multiple authors and users may create and delete pages in an ad hoc, unorganized manner. Wikis can provide one or more ways to categorize or tag pages to support the maintenance of such index pages. Some wikis, including the original, have a backlink feature, which displays all pages that link to a given page. It is also typically possible in a wiki to create links to pages that do not yet exist, as a way to invite others to share what they know about a subject new to the wiki. Wiki users can typically "tag" pages with categories or keywords, to make it easier for other users to find the article. For example, a user creating a new article on cold-weather biking might "tag" this page under the categories of commuting, winter sports and bicycling. This would make it easier for other users to find the article. Linking and creating pages Links are created using a specific syntax, the so-called "link pattern". Originally, most wikis[citation needed] used CamelCase to name pages and create links. These are produced by capitalizing words in a phrase and removing the spaces between them (the word "CamelCase" is itself an example). While CamelCase makes linking easy, it also leads to links in a form that deviates from the standard spelling. To link to a page with a single-word title, one must abnormally capitalize one of the letters in the word (e.g. "WiKi" instead of "Wiki"). CamelCase-based wikis are instantly recognizable because they have many links with names such as "TableOfContents" and "BeginnerQuestions." a wiki can render the visible anchor of such links "pretty" by reinserting spaces, and possibly also reverting to lower case. This reprocessing of the link to improve the readability of the anchor is, however, limited by the loss of capitalization information caused by CamelCase reversal. For example, "RichardWagner" should be rendered as "Richard Wagner", whereas "PopularMusic" should be rendered as "popular music". There is no easy way to determine which capital letters should remain capitalized. As a result, many wikis now have "free linking" using brackets, and some disable CamelCase by default. Searching Most wikis offer at least a title search, and sometimes a full-text search. The scalability of the search depends on whether the wiki engine uses a database. Some wikis, such as PmWiki, use flat files.[11] MediaWikicommas first versions used flat files, but it was rewritten by Lee Daniel Crocker in the early 2000s (decade) to be a database application.[citation needed] Indexed database access is necessary for high speed searches on large wikis. Alternatively, external search engines such as Google Search can sometimes be used on wikis with limited searching functions to obtain more precise results.