The time dimension of documents was not the priority
in the first solutions developed for multimedia web content.
Web formats have left aside the issue of synchronization for
a long time. Plug-ins did not allow the various components
of a web page to be synchronized with continuous media
through a standard API. The first step in this direction was
made with SMIL, with a rather radical approach: time is the
main (and almost the only) dimension for structuring a document.
As a consequence, the hierarchical structure offered
by other web formats for representing the logical organization
of documents can hardly be expressed with SMIL.