That means that all the behaviour in this widget has been specified declaratively.
If that does not make you curious then I am not sure what will :-)
This example shows how you can "ajaxify" an entire form simply adding in the attribute:
This is only recommended for simple forms as all the buttons within the form refresh the same zones.
Next we can see how to "ajaxify" the form buttons individually and specifying the zones to refresh for each of them:
This is the classic examples of dependable drop down lists, With AjaxAnywhere is extremely easy and clean to implement:
Normal links that are not associated with any form element can be "ajaxified" too. You can also check how AjaxAnywhere handles the possible redirects automatically: