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It used to be a PRO feature to use multiple external resources on a Pen. No more! That feature is now available to all users.
Not much more to say - we just thought that was a bit of an arbitrary restriction considering you're free to
<link> up additional stylesheets or
<script>s from the HTML anyway. Might as well not limit the ease of building awesome stuff.
We updated the documentation to reflect this, which includes information about using Pens-as-resources, which is a pretty cool feature that works great with this.