[facebook] Facebook share link - can you customize the message body text?

I'm trying to create a link that will share a page on Facebook. So far I've got:

href="http://www.facebook.com/sharer.php
?u=http%3A%2F%2Fwww.cnn.com%2F
&t=CNN%26s+website"

However, I'd really like to add some text that will go in the 'What's on your mind?' text box (especially as the t value gets overridden by the link's title). Does anyone know if this is possible?

NOTE: @azure_ardee solution is no longer feasible. Facebook will not allow developers pre-fill messages. Developers may customize the story by providing OG meta tags, but it's up to the user to fill the message.

This is only possible if you are posting on the user's behalf, which requires the user authorizing your application with the publish_actions permission. AND even then:

please note that Facebook recommends using a user-initiated sharing modal.

Have a look at this answer.

Like said in docs, use

<meta property="og:url"           content="http://www.your-domain.com/your-page.html" />
<meta property="og:type"          content="website" />
<meta property="og:title"         content="Your Website Title" />
<meta property="og:description"   content="Your description" />
<meta property="og:image"         content="http://www.your-domain.com/path/image.jpg" />

image size recommended: 1 200 x 630

Like @Ardee said you sharer.php uses data from the meta tags, the Dialog API accepts parameters. Facebook have removed the ability to use the message parameter but you can use the quote parameter which can be useful in a lot of cases e.g.

https://www.facebook.com/dialog/share?
app_id=[your-app-id]
&display=popup
&title=This+is+the+title+parameter
&description=This+is+the+description+parameter
&quote=This+is+the+quote+parameter
&caption=This+is+the+caption+parameter
&href=https%3A%2F%2Fdevelopers.facebook.com%2Fdocs%2F
&redirect_uri=https%3A%2F%2Fwww.[url-in-your-accepted-list].com

Just have to create an app id:

https://developers.facebook.com/docs/apps/register

Then make sure the redirect url domain is listed in the accepted domains for that app.

To add some text, what I did some time ago , if the link you are sharing its a page you can modify. You can add some meta-tags to the shared page:

<meta name="title" content="The title you want" />
<meta name="description" content="The text you want to insert " />
<link rel="image_src" href="A thumbnail you can show" / >

It's a small hack. Although the old share button has been replaced by the "like"/"recommend" button where you can add a comment if you use the XFBML version. More info her:

http://developers.facebook.com/docs/reference/plugins/like/

Simplest way to share on facebook is:
https://www.facebook.com/sharer/sharer.php?u=xerosanyam.github.io&quote=You_are_amazing

Bonus:
Simplest way to share on twitter is: https://twitter.com/intent/tweet?via=xerosanyam&text=You_are_amazing

Facebook does not allow you to change the "What's on your mind?" text box, unless of course you're developing an application for use on Facebook.