Caret navigation

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A caret flashing in a text entry box

In computing, caret navigation is a kind of keyboard navigation where a caret (also known as "text cursor", "text insertion cursor", or "text selection cursor") is used to navigate within a text document. It is a fundamental feature for applications that deal with text, for example text editors (the most famous examples: Microsoft Word, Emacs and Vim), word processors and desktop publishing programs.

This kind of navigation is also supported by some web browsers, such as Mozilla Firefox and Internet Explorer, where it is referred to as "caret browsing". This can be contrasted with the alternate and more usual control methods of using a mouse to point to links and select text for copying or editing, or using tabs to step through and highlight each link on the page in turn. It is however not a universally supported control method; notably, Google Chrome does not (as of November 2012) offer it as a built-in function.

In this text navigation mode, a blinking cursor appears over the text on-screen. The user can then move throughout the text by using the arrow navigation keys, and perform various actions to manipulate it, commonly including:

Caret navigation usually also incorporates a form of viewport scrolling control, where the caret moves freely within certain margins of a static display, but triggers a scrolling event on reaching one of the margins (either the edge of the screen/window/text field, or a point a certain number of lines/characters within said edge). For example, the view within a WYSIWYG word processor may scroll the whole viewport a certain amount down the page as the caret nears the lower edge of the edit window, in order to keep the text currently being entered or edited roughly centered without excessive, distracting and potentially computationally expensive line-by-line scrolling; similarly, a spreadsheet character-based word processor on a low-resolution screen may scroll in all directions, character-by-character or line-by-line, maintaining a small margin which the caret never enters in order to show the user what text or cells lie directly "ahead" of or "behind" the edit point and prevent them from "working blind".

In contrast, a plain text text entry form may use a simpler method, setting a fixed and arbitrary display width within which the caret always "wraps around", only scrolling up or down a line as the caret reaches the wrap point at the start/end of the current first/last line, in order to keep the edit point in view as it moves to the previous/next line of text; all other scrolling must be manually controlled by the user, by use of scroll bars, mouse wheel, or Page Up/Page Down keys. Another alternate form of control is used in some spreadsheets when the Scroll Lock key is activated; in this case the caret is locked to the centre of the screen, and the cursor keys instead move the worksheet itself "underneath" the static caret, instead of the caret moving "over" the sheet. Effectively, the margins that trigger a scrolling action are increased to their maximum possible size (vs the minimum possible with the web edit box), causing the caret to be recentred any time it attempts to move.

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