The examples (how it should look):
a relative link
an absolute (external) link 
a link with onclick
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For hyperlinks (a) the CSS for this page defines a few selectors, to give hyperlinks a distinct styling depending on what they point to.
On the right is what you should see. (if you just see a bunch of regular underlined hyperlinks on the left, your browser doesn't support advanced CSS selectors and/or CSS-generated content)
The examples (how it should look):
a relative link
an absolute (external) link
a link with onclick
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