General tools. Docs available here - Minimized source here
The YAHOO.Tools package now includes a version of Douglas Crockford's JSON.js file that doesn't mess with the object prototypes.
You can see an example of the JSON parser here.
YAHOO.Tools.getBrowserEngine();
This function attempts to identify the core browsers through object detection. However, a developer may trash this detection by adding "functionality" to a page.
Go ahead, change your User Agent string. This should still work 8-)
YAHOO.Tools.getBrowser();
This function uses the User Agent string to determine it's information. It will be fooled by a User Agent switcher