Inline links, such as the familiar A element
from HTML, are themselves part of the source or target of the
link. The source of the link, that is the blue underlined text, is
included inside the A element that defines the link.
Most simple links are inline.
An out-of-line link does not contain any part of any of the resources it connects. Instead, the links are stored in a separate document called the linkbase.
Out of line links allow you to add links to and from documents that can't be modified such as a page on someone else's web site.
Out of line links allow you to add links to different parts of non-XML content.
Out of line links are not yet supported by software.