This means that to use them semantically, divs should be used to wrap sections of a document, while spans should be used to wrap small portions of text, images, etc.
For example:
<div>This a large main division, with <span>a small bit</span> of spanned text!</div>
Note that it is illegal to place a block-level element within an inline element, so:
<div>Some <span>text that <div>I want</div> to mark</span> up</div>
...is illegal.
EDIT: As of HTML5, some block elements can be placed inside of some inline elements. See the MDN reference here for a pretty clear listing. The above is still illegal, as <span> only accepts phrasing content, and <div> is flow content.
You asked for some concrete examples, so is one taken from my bowling website, BowlSK:
<div id="header">
<div id="userbar">
Hi there, <span class="username">Chris Marasti-Georg</span> |
<a href="/edit-profile.html">Profile</a> |
<a href="https://www.bowlsk.com/_ah/logout?...">Sign out</a>
</div>
<h1><a href="/">Bowl<span class="sk">SK</span></a></h1>
</div>
Ok, what's going on?
At the top of my page, I have a logical section, the "header". Since this is a section, I use a div (with an appropriate id). Within that, I have a couple of sections: the user bar and the actual page title. The title uses the appropriate tag,
h1. The userbar, being a section, is wrapped in a
div. Within that, the username is wrapped in a
span, so that I can change the style. As you can see, I have also wrapped a
span around 2 letters in the title - this allows me to change their color in my stylesheet.
Also note that HTML5 includes a broad new set of elements that define common page structures, such as article, section, nav, etc.
Section 4.4 of the HTML 5 working draft lists them and gives hints as to their usage. HTML5 is still a working spec, so nothing is "final" yet, but it is highly doubtful that any of these elements are going anywhere. There is a javascript hack that you will need to use if you want to style these elements in some older version of IE - You need to create one of each element using document.createElement before any of those elements are specified in your source. There are a bunch of libraries that will take care of this for you - a quick Google search turned up html5shiv.
Assume your iFrame's id is "targetFrame" and the function you want to call is targetFunction():
document.getElementById('targetFrame').contentWindow.targetFunction();
You can also access the frame using window.frames instead of document.getElementById.
// this option does not work in most of latest versions of chrome and Firefox
window.frames[0].frameElement.contentWindow.targetFunction();
Best Solution
The difference is an iframe is able to "float" within content in a page, that is you can create an html page and position an iframe within it. This allows you to have a page and place another document directly in it. A
framesetallows you to split the screen into different pages (horizontally and vertically) and display different documents in each part.Read IFrames security summary.