The $:/core/images/file needs to have some namespace stuff after <svg... I just pasted in the namespace from the fishes (xmlns="
http://www.w3.org/2000/svg" xmlns:xl="
http://www.w3.org/1999/xlink" ). And it needs to have the type, which is unset by default, set to images/xml+svg .
I don't know if these changes will "spoil" $:/core/images/file for some other use, so it might be safer to clone the tiddler, make the changes to the clone, and then use the clone.
As an aside, I just discovered that
tw.com is a real web site, and has nothing to do with TiddlyWiki.
-- Mark