The 1st wave of Microsoft ASP.NET AJAX Control to master

There are and will be many and many AJAX controls, some of them are the essentials and the mostly used. 主要是关于Panel的“基层”control，我称之为“Panel Group”吧。Thus, learn to use them in the first wave:

d UpdatePanel

这个是最基本的。专门研究吧。

d PopupControl
PopupControl is an ASP.NET AJAX extender that can be attached to any control in order to open a popup window that displays additional content.
This popup window will probably be interactive and will probably be within an ASP.NET AJAX UpdatePanel, so it will be able to perform complex server-based processing (including postbacks) without affecting the rest of the page.
The popup window can contain any content, including ASP.NET server controls, HTML elements, etc..
Once the work of the popup window is done, a simple server-side call dismisses it and triggers any relevant script on the client to run and update the page dynamically.
^ 这是个基本的control，也是比较原始意义的AJAX功能，用途比较广泛。比如填写某个TextBox的时候，可以探出一个小Panel用于选择日期，计算某些数等等。

d HoverMenu
HoverMenu is an ASP.NET AJAX extender that can be attached to any ASP.NET WebControl, and will associate that control with a popup panel to display additional content.
^ 我觉得HoverMenu这个名字起得不好，不如叫HoverPopupPanel。这种功能倒是会用得挺多，比如用于当鼠标滑到某个位置的时候，弹出一个圆角小方框显示文字。

d CollapsiblePanel
The CollapsiblePanel is a very flexible extender that allows you to easily add Collapsible sections to your web page. This extender targets any ASP.NET Panel control.
The page developer specifies which control(s) on the page should be the open/close controller for the panel, or the panel can be set to automatically expand and/or collapse when the mouse cursor moves in or out of it, respectively.

d Accordion
The Accordion is a web control that allows you to provide multiple panes and display them one at a time. It is like having several CollapsiblePanels where only one can be expanded at a time.
The Accordion is implemented as a web control that contains AccordionPane web controls. Each AccordionPane control has a template for its Header and its Content. We keep track of the selected pane so it stays visible across postbacks.

d DynamicPopulate
DynamicPopulate is a simple extender that replaces the contents of a control with the result of a web service or page method call. The method call returns a string of HTML that is inserted as the children of the target element.
^ 这应该最原始意义上的AJAX功能。