In article , Martin Gregorie
 wrote:

> On Sun, 16 Aug 2020 03:05:35 +0200, Axel Berger wrote:
>
> > Martin Gregorie wrote:
> >> They are generally NOT added by the web page's author:
> >
> > We're beginning to lose ourselves into semantics here. The page's author
> > is the one who wrote that which leaves the server and arrives at the
> > browser: the HTML, CSS, JS etc. Whether he wrote static code or a
> > program generating it only a question of tools. If I decide to quote a
> > poem of Goethe's on one of my web pages, that doesn't make Goethe the
> > page's author. If the "free" servers work as you say, I wouldn't know,
> > then you are not the author of the page, but its true author generously
> > allows you to add a bit of prose of yours to *his* page.
>
> I was being specific here, deliberately describing something everybody
> has seen:a Wikipedia page.  Here the page content (text and images) is
> obviously written by a volunteer editor and sits in some sort of datastore
> in more or less the format that its author and contributors hit save on.
> This is what I meant by the 'page content' When a page is requested, more
> stuff gets added:
>
> - the standard Wikipedia header and footer (not written by the author,
>   but no more contentions than the content of the HTML  section).
>   These always have the same format but not written by the page author.
>
> - the half screenful of donation request that gets added every time
>   Wikipedia needs more cash. To me this is no different to any other
>   advert, and again is not written or supplied by the page author.
>
> I'm only describing it this way to emphasize to the OP that a web server
> can and does inject additional material into a web page before it is sent
> to the browser.

And you've got it wrong, as a few others have already tried to point
out.

I will try to make the case clearer.

A better example than Wikipedia would be a newspaper website in the
current era. First, it is entirely possible to have multiple articles
(or their abstracts) written by different content experts on a single
web page. Further, as you note, the content expert's contribution is
probably stored somewhere off in a database. It may be displayed on
many pages, in any number of formats, possibly syndicated across
different newspaper websites, and the content expert need have no
specific knowledge of this. Indeed, each of those pages displaying the
expert's contribution might be unique because of the non-expert- or
different-expert-content on the page. It makes no sense to say that a
content expert has authored any of these pages.

What you seem to be trying to describe with "injection" (which I agree
with a previous poster is a misuse of the term) are simply dynamic web
pages. Page schemas are assembled first on the server, possibly from
many components fetched from different sources, according to a
prescription created by what one might consider the page author. (The
author need not be a single individual and there very well may be no
corresponding html file, anywhere). The layout may be simple, say
header/content/footer, the richness of the page would then arise from
the content of the components, which may come from different parts of
an organization or different organizations (including, e.g., ad
vendors). The page author probably knows very little about the
components, including those contributed by content experts, except to
allocate each its own bit of real estate on the page.

The schema constructed by the server is fetched by the user's browser
-- which continues the page assembly process by fetching further
content, again possibly from widely varying sources (which certainly
may include servers other than that from which the page schema was
served). The result is a webpage seen by the user which, again, may be
unique to that user on that browser at that particular moment.

To a good approximation, I believe a user navigating the web today will
encounter 100% dynamic pages. Dynamic pages are not the exception, they
are the rule.

The "standard Wikipedia header" as a model for web pages is largely
incorrect and certainly misleading. The headers and footers (and other
components) may be highly customized for the particular user viewing
them (and there's a whole industry focussed entirely on doing just
that). I can assure you that retail websites put a great deal more
time/effort/money into this customization than they do into fronting a
title for a product, its image, it's SKU, and an "Add to Cart" button
in the center of a page, necessary though that is. The Wikipedia
request for donations is a simple example of such customization but it
misrepresents what, in general, is going on with pages and their
construction: there may be much more complexity to the construction of
headers and footers than in what the user perceives as the content of a
page. And of course none of this happens unless the page author
provides for it.

> - code such as ad-blockers running in the browser can and does prevent
>   the content these tags reference from being displayed, but cannot
>   inject text, image selection tags, etc that were not on the HTML page
>   sent by the server

Untrue for the past 20 years or more. A page can download arbitrary
Javascript which can then alter the page via the DOM to do just about
anything one could imagine, including change HTML tags or their
contents on the fly. (You used to be able to find some examples of
crude web page animations using this method around the Internet - I
haven't actually seen these myself for quite a while).

Another issue. Apache does serve files, e.g., images, but most of the
non-image content a user sees will come from one of many application
servers (probably on the other side of an inner-tier firewall from
Apache). Applications on these servers receive requests forwarded from
Apache and return responses to those requests for Apache to return to
the user's browser. Apache serves in a central role but it is largely a
pass-through for much of the non-image web content.

Design, construction and operation of a modern website is very
different than dropping some static html and image files into Apache's
Documents directory and then typing 'apachectl'. Lots of people have
been working on them for 30 years, after all.

   Tom

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