External links

I am viewing this document with Firefox's internal pdf viewer, which results in opening all external links in the same tab as the document itself.

See https://en.wikibooks.org/wiki/LaTeX/Hyperlinks#Customization for the option `pdfnewwindow`
```quote
define if a new window should get opened when a link leads out of the current document
```

I am not sure if one should add this option to
  `fonts/opensans/doc/fonts/opensans/opensans.tex`
too.