<BASE> | NN all IE all HTML all
<BASE> | End Tag: Forbidden
A BASE element is defined inside a document's HEAD element to instruct the browser about the URL path to the current document. This path is then used as the basis for all relative URLs used to specify various SRC and HREF attributes in the document. The BASE element's URL should be a complete URL, including the document name. The browser calculates the base URL path to the directory holding that document. For example, if you specify <BASE HREF="http://www.megacorp.com/products/index.html">, the HREF attribute of a link on that page to widgets/framitz801.html resolves to the full URL of http://www.megacorp.com/products/widgets/framitz801.html. Similarly, a relative URL can walk up the hierarchy with the dot syntax. For example, from the BASE element defined earlier, an IMG element in the index.html page might be set for SRC="../images/logo.jpg". That reference resolves to http://www.megacorp.com/images/logo.jpg. By and large, today's browsers automatically calculate the base URL of the currently loaded document, thus allowing use of relative URLs without specifying a BASE element. This is especially helpful when you are developing pages locally and don't want to change the BASE element settings when you deploy the pages. The HTML 4.0 specification states that a document lacking a BASE element should by default use the current document's URL as the BASE URL. Of course, this is only for true web pages, rather than HTML-enhanced documents such as email messages, which have no default BASE URL. You can also use the BASE element to define a default target for any link-type element in the document. Therefore, if all links are supposed to load documents into another frame, you can specify this target frame once in the BASE tag and not worry about TARGET attributes elsewhere in the document. If you wish to override the default for a single link, you may do so by specifying the TARGET attribute for that element.
Example
    <HEAD>
    <BASE HREF="http://www.megacorp.com/index.html" TARGET="_top">
    </HEAD>
Object Model Reference
IE | [window.]document.all.elementID

HREF | NN all IE all HTML all
HREF="URL" | Optional
The HREF attribute is a URL of a document whose server path is to be used as the base URL for all relative references in the document. This is typically the URL of the current document, but it can be set to another path if it makes sense to your document organization and directory structure.
Example
    <BASE HREF="http://www.megacorp.com/products/index.html">
Value This should be a full and absolute URL to a document.
Default | Current document pathname.
Object Model Reference
IE | [window.]document.all.tags("base")[0].href

TARGET | NN all IE all HTML 4
TARGET="windowOrFrameName" | Optional
If all or most links and area maps on a page load documents into a separate window or frame, you can set the TARGET attribute of the BASE element to take care of targeting for all of those elements. You can set the TARGET attribute without setting the HREF attribute if you want to set only the base target reference.
Example
    <BASE TARGET="rightFrame">
Value Case-sensitive identifier when the frame or window name has been assigned via the target element's NAME attribute. Four reserved target names act as constants:
_blank | Browser creates a new window for the destination document.
_parent | Destination document replaces the current frame's framesetting document (if one exists; otherwise, it is treated as _self).
_self | Destination document replaces the current document in its window or frame.
_top | Destination document is to occupy the entire browser window, replacing any and all framesets that may be loaded (also treated as _self if there are no framesets defined in the window).
Default | _self
Object Model Reference
IE | [window.]document.all.tags("base")[0].target