baseuri

baseURI refers to the base Uniform Resource Identifier used to resolve relative URLs within a document. It represents the absolute URL against which any relative links, scripts, images, and other resources are resolved. In many contexts, baseURI can be determined by the document's own URL, a base element, or an xml:base attribute, and is exposed by the document object model as a property that can be read for a given node.

In HTML, the base element in the head can set the document’s base URL with its href attribute. When present, relative URLs in the document—such as those in anchor hrefs, image src attributes, and form actions—are resolved against this base URL. If no base element is provided, the document’s own URL serves as the base. It is customary to include only one base element with a defined href; browsers typically use the first such base and ignore later ones.

In XML, the xml:base attribute can be applied to elements to specify a base URI for resolving relative URIs within that element’s scope. The effective base URI is determined by the nearest ancestor’s base, allowing different parts of a document to use different bases when necessary. The DOM’s Node.baseURI property reflects this resolution, offering a programmatic way to obtain the absolute base.

Practical notes include the impact on resource loading and link resolution. Changing the base URI can alter how relative links are interpreted, which is useful in templating and multi-resource documents but can lead to broken links if not managed consistently. Absolute URLs in attributes override the base URI, as they do not rely on relative resolution.