Demand an xmlns:id=Value in the outer html tag. This uses the
html_post/2 mechanism to post to the xmlns channel. Rdfa
(http://www.w3.org/2006/07/SWD/RDFa/syntax/), embedding RDF in
(x)html provides a typical usage scenario where we want to
publish the required namespaces in the header. We can define:
rdf_ns(Id) -->
{ rdf_global_id(Id:'', Value) },
xhtml_ns(Id, Value).
After which we can use rdf_ns//1 as a normal rule in html//1 to
publish namespaces from library(semweb/rdf_db). Note that this
macro only has effect if the dialect is set to xhtml. In
html mode it is silently ignored.
The required xmlns receiver is installed by html_begin//1
using the html tag and thus is present in any document that
opens the outer html environment through this library.
