For any file type where the handler returns true from mustRender(), such as SVG, PDF, DjVu, etc., the renderer is required to not attempt to link directly to the file in an <img/> tag. For example, for wikitext input [[File:Cross.svg]], the MW output is
<a href="/wiki/File:Cross.svg" class="image"><img alt="Cross.svg" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Cross.svg/32px-Cross.svg.png" width="32" height="32" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Cross.svg/48px-Cross.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Cross.svg/64px-Cross.svg.png 2x" data-file-width="32" data-file-height="32" /></a>
whereas Parsoid attempts client-side scaling regardless of the file type:
...<img resource="./File:Cross.svg" src="//upload.wikimedia.org/wikipedia/commons/8/8b/Cross.svg" data-file-width="32" data-file-height="32" data-file-type="drawing" height="32" width="32" data-parsoid='...'/>