You can embed external svg via an img @src attribute, for example the html5 svg logo
Apparently, you can also embed cells directly from observablehq, like this one from the Observable Guide to Downloading and Embedding Notebooks:
(I learnt this via this (interesting) discussion on twitter)
And (because twitter doesn't allow vizhub to view the page within an iframe) I'm opening in another tab, and thanks to this post on how to Open Link in a New Window and this post on injecting code around links with css I have added a css-driven world icon to indicate a link is to an external website and arrow-icons to show that links will be opened in a new tab / the parent window / the top window
More link + css fun
It is also interesting to note that HTML5 DOES support the href target attribute (again).
Test break out of iFrame (target parent window)
Tip: you don't need to define the top anchor anymore!
According to the article How to create a link that goes to the top of a web page modern browsers understand href="#top" automatically!
... but, of course, the automatic top goes to the top of the ENTIRE browser page ... causing a lovely (?) recursion...