> My understanding of parameter entities is that they are only allowed within
> a markup declaration, not a document instance. How this might work for HTML
> I don't know -- I wouldn't want to break SGML conformance to allow
> parameter entities within HTML documents.
As I read it, the declaration of a parameter entity can occur within a
document instance but must be within the <!doctype declaration, eg
<!doctype html system "/dtdlib/html3.dtd" [
<!entity % mybullet system "pix/redbull.gif">
<!entity % regform system "forms/regform.html">
It can then be referenced at any subsequent stage.
<h1><img src="&mybullet;"> Foo Bar's Grill & Deli</h1>
<p>You ain't seen nuthin' yet...fill in the form:</p>
(I hope I've got this right, someone's gone off with my Goldfarb, so
I'm not certain is what I've described is totally kosher.)
The use of parameter entities was the mechanism proposed in Nov 1983
to let users specify in advance the content of frequently-occurring
entities, or those entities like external files which might change name
over time, and this lets you find the definition easily because it's at
the top of the instance, rather than buried 6 feet deep in markup.