Via Pedro Serrano:
Features include :
- Explore and modify the document object model (DOM) of a web page.
- Locate and select specific elements on a web page through a variety of techniques.
- Selectively disable Internet Explorer settings.
- View HTML object class names, ID’s, and details such as link paths, tab index values, and access keys.
- Outline tables, table cells, images, or selected tags.
- Validate HTML, CSS, WAI, and RSS web feed links.
- Display image dimensions, file sizes, path information, and alternate (ALT) text.
- Immediately resize the browser window to 800×600 or a custom size.
- Selectively clear the browser cache and saved cookies. Choose from all objects or those associated with a given domain.
- Choose direct links to W3C specification references, the Internet Explorer team weblog (blog), and other resources.
- Display a fully featured design ruler to help accurately align objects on your pages.
This may come in handy when trying to determine which CSS-class to modify when customizing the look-and-feel of a SharePoint-site or site definition template set. And ofcource for any kind of HTML editing/analyzing purposes.