HTML and CSS Reference
abled icons and dingbats, including animated images, can be effective
visual guides to internal and external resources. If an image doesn't do
any of these valuable services for your document, throw it out already!
One of the most important considerations when adding images to a doc-
ument is the additional delay they add to the retrieval time for a doc-
ument over the network, particularly for modem connections. While a
common text document might run, at most, 10,000 or 15,000 bytes,
images can easily extend to hundreds of thousands of bytes each. And
the total retrieval time for a document is not only equal to the sum of
all its component parts, but also to compounded networking overhead
Depending on the speed of the connection ( bandwidth , usually ex-
pressed as bits or bytes per second) as well as network congestion that
can delay connections, a single document containing one 100 KB image
may take less than a second through a cable modem connection in the
wee hours of the morning, when most everyone else is asleep, to well
over 10 minutes with a cell phone at noon. You get the picture?
With that said, of course, pictures and other multimedia are driving In-
ternet providers to come up with faster, better, more robust ways to
deliver web content. Modem connections are quickly going the way of
the horse and carriage, replaced by technologies like high-speed cable
modems and the Asymmetric Digital Subscriber Line (ADSL).
Still, as the price lowers, use goes up, so there is the issue of conges-
tion. And don't forget cell phone browsers and our Third World neigh-
bors, where connections are spotty and slow. Besides, if you are com-
peting for access to an overburdened server, it doesn't matter how fast
your connection may be.
5.2.3. When to Use Text
Text hasn't gone out of style. For some users, it is the only accessible
portion of your document. We argue that, in most circumstances, your
documents should be usable by readers who cannot view images, or
have disabled automatic download in their browsers to improve their