HTML hover is an event generated by user input when the mouse cursor stops over an element in a web page. It can trigger various effects, captured by CSS or JavaScript. Navigational assistance and aesthetic purposes are common uses, but malicious code can also exploit it.
Within a web browser displaying a HyperText Markup Language (HTML) document, an HTML mouseover is an action or event generated through user input. By definition, an HTML hover is what happens when the mouse cursor on a screen stops over an element within the web page, triggering a hover event that code placed within the web page can respond to. The actual effect can be anything from displaying navigation text to changing an image to make it appear highlighted, or even changing a few separate properties on the web page. Some web browsers and operating systems define a hover event slightly differently, so selections using the TAB key on a keyboard will also be considered hover. HTML hover events are typically captured using cascading style sheet (CSS) code, JavaScript® functions, or a combination of both, since basic HTML doesn’t have the ability to directly interact with a suspended cursor.
Most computer operating systems that accept user input actually break down any seemingly simple action into a sequence of steps or events. Web browsers must be able to interpret and respond to these events so that users can interact with a web page. These events are generated by the computer system in response to a user action, passed to the web browser, and then rendered available to all active programs that are listening for events attached to the HTML page.
When a mouse cursor hovers over an element in an HTML document, it actually fires at least three separate events. The first is when the mouse initially makes contact with the element, known as an enter or onMouseEnter event. The last event raised when the mouse leaves the element is called the exit or onMouseExit event. The amount of time the mouse is inside the element between these two events is known as hovering and raises an HTML hover event. One thing to note about hovering is that a mouse doesn’t always have to be perfectly still to be considered hovering, the event can be triggered automatically by simply entering the element space.
Navigational assistance is a common use for an HTML hover event, which causes informational text to appear at the location of the mouse cursor when a link or image is passed. It can also be used to provide short textual definitions of words in a document. More often, it’s used for aesthetic purposes, like animating graphic dials or arrows when the mouse brings them into focus. While there are many security precautions to prevent this, malicious code in particular can sometimes use an HTML hover event over an empty space on a web page to pop up windows outside the web browser.
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