Adding a Subject Line to an Email Link

I am always surprised with the little simple things I learn about web development. After years of working with HTML I had not yet seen the simple coding for adding a subject line to an email link. Normally the code for an email link looks like this:

<a href="mailto:friend@yourdomain.com">mailto</a>

If you write it like this:

<a href="mailto:friend@yourdomain.com?My Special Subject">
mailto</a>

Then when it is clicked the email will have a subject of "My Special Subject."