Modern HTML commonly uses CSS and Javascript. This requires <link> elements in the HTML <head> element or <script> elements in the <body>. Unfortunately this seriously harms re-using HTML DCG rules as components as each of these components may rely on their own style sheets or JavaScript code. We added a‘mailing’system to reposition and collect fragments of HTML. This is implemented by html_post//2, html_receive//1 and html_receive//2.
//\-commands are executed by mailman/1
from print_html/1 or html_print_length/2.
These commands are called in the calling context of the html_post//2
call.
A typical usage scenario is to get required CSS links in the document head in a reusable fashion. First, we define css//1 as:
css(URL) -->
html_post(css,
link([ type('text/css'),
rel('stylesheet'),
href(URL)
])).
Next we insert the unique CSS links, in the pagehead using the following call to reply_html_page/2:
reply_html_page([ title(...),
\html_receive(css)
],
...)
////phrase(Handler, PostedTerms, HtmlTerms, Rest)
Typically, Handler collects the posted terms, creating a term suitable for html//1 and finally calls html//1.
The library predefines the receiver channel head at the
end of the
head element for all pages that write the html head
through this library. The following code can be used anywhere inside an
HTML generating rule to demand a javascript in the header:
js_script(URL) -->
html_post(head, script([ src(URL),
type('text/javascript')
], [])).
This mechanism is also exploited to add XML namespace (xmlns)
declarations to the (outer) html element using xhml_ns//2:
//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.