RPubs documents are currently displayed verbatim as they are uploaded by users. This may cause issues with external links to sites that do not allow their pages to be shown in a frame.
You can fix this issue by adding the following line to your document:
<base target="_top"/>
If you'd prefer to specify for individual links, you can set links to open external pages by adding the following to your link HTML:
<a target="_top"/>
For example, a link to GitHub would then look like this:
<a href="http://www.github.com" target="_top"/>Github</a>