An experiment by Scott Jehl of Filament Group
Here is an inline (embedded) SVG graphic. It was loaded from an external file called signal.svg.
To load and embed the SVG file, this page includes the following markup:
<iframe src="signal.svg" onload="this.before(this.contentDocument.children); this.remove();"></iframe>
However, if you inspect the graphic above using developer tools, you'll see the SVG markup for the icon, inlined right in the HTML DOM, with no iframe element to be found. This is because the code uses an iframe to load the SVG file, and an onload event to inject the iframe's document just before the iframe in the HTML, before deleting the iframe itself.