SVG files are smaller than PNG files, can be compressed, and are
scalable.
We're choosing to render SVG files as images instead of inline because
inline SVGs aren't cached nor compressed, and they might appear several
times on the same page, making the generated HTML much larger.
We could also load them with an SVG sprite, using `<use>`, which would
reduce the number of HTTP requests when several icons are present on the
page (like in the index of most sections). However, using SVG inside an
`<img>` tag is universally supported, while the `<use>` tag doesn't
work in Internet Explorer when using an external URI and support in
Opera Mini and UC Browser is unknown.
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