base
Establishes a base file path for hyperlinks (href's); uncommon in eBooks. If you use this tag, <base> must be the first element in the heading, and the URL must be explicit.

attributes

href
URL of base. For instance, <base href="file://E:\my_books\" /> or <base href="E:\my_books\" /> declaration makes a reference within the body shorter:
<img src="pic/title.jpg" /> instead the complete source path for the image "E:\my_ books\pic\title.jpg"