Adobe® Dreamweaver® CS5 behaviors place JavaScript code in documents so that visitors can change a web page in various ways or initiate certain tasks.
A behavior is a combination of an event and an action triggered by that event.
In the Behaviors panel, you add a behavior to a page by specifying an action and then specifying the event that triggers that action.
Behavior code is client-side JavaScript code; that is, it runs in browsers, not on servers.
Events are, effectively, messages generated by browsers indicating that a visitor to your page has done something. For example, when a visitor moves the pointer over a link, the browser generates an onMouseOver event for that link; the browser then checks whether it should call some JavaScript code (specified in the page being viewed) in response. Different events are defined for different page elements; for example, in most browsers onMouseOver and onClick are events associated with links, whereas onLoad is an event associated with images and with the body section of the document.
An action is pre-written JavaScript code for performing a task, such as opening a browser window, showing or hiding an AP element, playing a sound, or stopping an Adobe Shockwave movie. The actions provided with Dreamweaver provide maximum cross-browser compatibility.
After you attach a behavior to a page element, the behavior calls the action (JavaScript code) associated with an event whenever that event occurs for that element. (The events that you can use to trigger a given action vary from browser to browser.) For example, if you attach the Popup Message action to a link and specify that it will be triggered by the onMouseOver event, then your message pops up whenever someone places the pointer over that link.
A single event can trigger several different actions, and you can specify the order in which those actions occur.
Dreamweaver provides about two dozen actions.
See Applying built-in Dreamweaver behaviors.
Additional actions can be found on the Exchange website at www.adobe.com/go/dreamweaver_exchange as well as on third-party developer sites. You can write your own actions if you are proficient in JavaScript.
Note: The terms behavior and action are Dreamweaver terms, not HTML terms. From the browser’s point of view, an action is just like any other piece of JavaScript code.
— About JavaScript Behaviors @ adobe.com
