HTML and CSS Reference
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.
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.
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
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).