XLinks can do everything HTML links can do and quite a bit more, but they aren't supported by current applications.
XLink elements of all types are placed in the http://www.w3.org/XML/XLink/0.9 namespace, normally with the xlink prefix. However, the URI is likely to change in future revisions to XLink.
Simple links behave much like HTML links, but they are not restricted to a single <A> tag.
Link elements are identified by xlink:type attributes.
Simple link elements are identified by xlink:type attributes with the value simple. The xlink:simple element is also a simple link.
Link elements can describe the resource they're linking to with title and role attributes.
Link elements can use the show attribute to tell the application how the content should be displayed when the link is activated, for example, by opening a new window.
Link elements can use the actuate attribute to tell the application whether the link should be traversed without a specific user request.
Extended link elements are identified by xlink:type attributes with the value extended. The xlink:extended element is also an extended link.
Extended links can contain multiple locators and arcs. Currently, it's left to the application to decide how to choose between different alternatives.
Locator elements are identified by xlink:type attributes with the value locator. The xlink:locator element is also a locator element.
A locator element has an href or xlink:href attribute whose value is the URI of the resource it locates.
Arc elements are identified by xlink:type attributes with the value arc. The xlink:arc element is also an arc element.
Arc elements have from and to attributes of IDREF type that identify to the locator elements they connect.
Arc elements may have show and actuate attributes to determine when and how traversal of the link occurs.
An extended link group element contains a list of links that connect a particular group of documents.
An extended link group element is identified by an xlink:type attribute with the value group. An xlink:group element is also an extended link group element.
An out of line link is an XLink (most commonly an extended XLink) that is not part of any of the documents it connects. Instead, the links are stored in a separate linking document.
An extended link document element is identified by an xlink:type attribute with the value document. An xlink:document element is also an extended link document element.
Each extended link document element has an href or xlink:href attribute whose value is the URI of the document.