At 04:08 PM 6/29/2005, Jack Keller wrote:
This is a question that I am curious about, I normally layout everything
with #idname but I've noticed here and there different tutorials using
div.classname instead for positioning.
Both seem to work, the class system seems to work easier, can anyone
explain the positives and/or negatives to either or both approaches?
Jack,
I'd say neither id nor class "works more easily" as a generic
statement. Like a hammer and a screwdriver, neither is better generally,
but they're each better than the other at performing specific tasks.
Ids must be unique on the page, classes need not be.
Ids are handy for pinpointing a specific item, or lassoing all the children
of a specific parent. Classes are handy for describing a number of items
that share certain attributes.
An element can have only one id but can have multiple classes:
<p id="intro" class="body sidebar">
That paragraph would be affected by any of these rules:
p#intro {}
p.body {}
p.sidebar {}
p#intro.sidebar {}
p.sidebar.body {} <== IE will see only the last class listed
Finally, ids have a greater valence in computing CSS specificity than
classes, so that in this instance:
p#intro { color: #F00; }
p.sidebar { color: #00F; }
The id rule will override the class rule, even though it comes first,
because ids "weigh" more than classes.
You should definitely read the CSS 2.1 specification entirely, but focusing on:
http://www.w3.org/TR/CSS21/selector.html
If you google +css +classes +ids you'll come up with tons of explanations,
such as:
http://www.tizag.com/cssT/cssid.php
Regards,
Paul
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