Currently, the quality filter only asks that you have a code block before it will accept your submission of a post containing a jsFiddle link. Without a block of code, the submission is rejected with an instruction.
Unfortunately, it doesn't matter what you put in that code block, as long as at least one line of text begins with four spaces to make an indented block of code in Markdown and isn't entirely whitespace. This means as long as you have a non-whitespace code block somewhere in your post, you can submit it with a fiddle link. It doesn't have to be actual code.
You can see an example question here, with a fiddle link and a single-line code block with the text "code" (and some explanatory text that's probably not too relevant):
code
There are other examples off the top of my head such as
.
and
enter code here
and
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and, well, code blocks that don't otherwise contain anything looking remotely like meaningful source code or output.
I know some users choose to work around the quality filter by posting gibberish as normal text instead of code, but that's a different issue, and one that doesn't really help users submit posts only containing fiddle links anyway.
The system already has something in place for detecting unindented code blocks, and from what I've seen it works pretty well. Would it be reasonable to use the same (or a similar) algorithm to check if a submission containing a jsFiddle link also contains a meaningful code block, so as to block at least some of the most egregious attempts at circumventing that aspect of the quality filter?
\@ -> \sf\@m
a meaningful code? It doesn't look so, yet it is ;) (and: codes in comments should have gray background.)