HTML and CSS Reference
In-Depth Information
seamless
: A Boolean attribute that, when present, indicates that the browser should render the
inline frame in a way that makes it appear to be part of the containing document. For example, a
seamless frame might apply CSS styles from the parent document before styles specified in the
framed document, and links in the contained document could open pages in the parent browsing
context rather than within the
iframe
(unless another setting prevents this). This effectively
embeds the external content into the rendered page, but does not embed the external markup
into the current HTML document. There aren't any browsers that support the
seamless
attribute
as of this writing.
src
: The URL of the page to embed. This can be either a relative or absolute URL, and doesn't
have to be a page within the same domain as the parent document.
srcdoc
: The content of the page that the embedded context is to contain. If
src
and
srcdoc
are
both specified,
srcdoc
takes precedence and
src
acts as fallback for browsers that don't support
the
srcdoc
attribute.
width
: The width of the frame in pixels.
The
iframe
element has been around for a long time, and older versions of HTML
offered other, similar framing devices as well. The
frameset
and
frame
elements were
introduced in HTML 4 and proved popular with web designers, but they were also
extremely problematic and inaccessible, and ultimately did more harm than good.
Window frames and inline frames were excluded entirely from XHTML 1.0 Strict. Old-
school frames are still dead in HTML5 (and good riddance), but
iframe
has been
renewed and revised, largely due to just how very useful it is and how commonplace it is
on the Web.
Lists
A list is simply a collection of two or more related items. A list consisting of a single item is perfectly valid
and may even be semantically correct in some cases, but normally a list groups several items together.
There are three types of lists in HTML: unordered lists, ordered lists, and description lists.
ul
An unordered list, designated by the
ul
element, is a list wherein the sequence of the items isn't especially
significant, such as a list of ingredients—the order in which you fetch them from the pantry doesn't matter
so long as you get everything on the list. Each list item is in turn defined by its own
li
element, all
contained by the surrounding
<ul>
and
</ul>
tags. The
ul
element is flow content and only
li
elements
are allowed as its children; no text or other elements can appear in an unordered list unless an
li
contains
them.
Listing 4-21 shows the ingredients for a cake recipe in an unordered list, with each item living in its own
li
element (more on that one in a moment).