Why does external link text contain punctuation?

While editing this site's markdown, you might come across external link text containing punctuation like this:

... see [Dart tools.](...)

Site pages are postprocessed so that external links become decorated with an "external link" icon, like this:

...

The text is visually more cohesive when the "external link" icon comes after the punctuation.

We should eventually get the tooling to handle this for us, but for now, you'll have to add the punctuation to the link text manually.