Figure 6. Sequence of linked biology pages: a, unlinked PDF
page; b, same page with links added by the link service via the project's
PDF plug-ins; c, a single link can point at multiple destinations;
d, following a link on 'embryo' to the Dictionary of Cell Biology,
a remote resource (note how this resource also has links added to it by
the link service, so although it is remote it can still be an integral
element of the linked Open Journal)