Since the SVG mime type (image/svg+xml) starts with image/, the AttachmentController lets it be displayed in the browser rather than download.  However, SVGs can contain javascript and other insecure components.
https://www.hackinparis.com/slides/hip2k11/09-TheForbiddenImage.pdf
https://www.w3.org/wiki/SVG_Security
Nice tests :)
Merged.