I saw that this edit was allowed to pass, even through visually it doesn't comply with the minimum character limit. They indeed are not rejected by the system and I don't think this is the intended behavior since normally there are so much wrong with a tag wiki, that a simple whitespace don't cut it.
This is not a bug, it's intended behavior, and it should not change.
The 6-character minimum was something that Jeff imposed, after initial high-level goals that included preventing suggested edits that were “extremely tiny in size”. I don't think he ever gave a precise reasoning for why 6 characters, or why tiny edits are problematic at all; mainly, he was against “a continal stream of character-twiddling edit suggesting users”. The character minimum has been often contested, and an additional mechanism to prevent “tiny” edits, the “too minor” rejection reason, was removed.
I don't have an official reference for not applying the 6-character minimum to tag wikis, but it's been in place for years and it's well-known, so it's clearly not a bug, it's the desired behavior.
I see three potential problems with too minor edits:
- Minor edits bump the post, and bumping posts that don't need attention drowns out the posts that do. That doesn't apply to tag wikis.
- They use up reviewers' time. When suggested edits were first introduced, that was a major problem — especially on Stack Overflow, the suggested edit queue was always clogged (not quite to the same level as the close review now, but close). Nowadays this isn't a problem, there are more people willing to review suggested edits than review tasks.
- Editors earn reputation, and that shouldn't be given out for no effort. Given that the amount of reputation earned is tiny (2 per edit), capped (at 1000), and that effort isn't really corellated to size, this isn't a good reason to put a hard limit on edits.
Tag wikis are meant to be widely useful, so they should be in the best possible shape. It would make no more sense to restrict edits to tag wikis than to Wikipedia articles. Since there is no systemic reason to apply additional restrictions to suggested edits, there should not be a character restriction.
One of the justifications given for keeping the 6-character minimum is that (if you have 50 rep) you can comment on the post to signal a desirable edit. This escape route is not available at all in tag wikis, reinforcing the desirability of allowing suggestions with no arbitrary threshold.
normally there are so much wrong with a tag wiki, that a simple whitespace don't cut it.
That's rather absurd for many reasons. Yes, there's always room for improvement, but improvement comes one thing at a time. Then you go from requiring non-whitespace changes to requiring a minimum character limit, which is pretty drastic. And there are cases where a whitespace edit is needed to get the formatting right.
As for the specific suggestion you cite, which appears to only change whitespace, I suspect it's an involuntary side effect of editing the wiki body. Sometimes editing the body causes whitespace normalization in the excerpt. It's a bug that the normalization isn't either ignored or performed silently.
This edit is of course too short, and should have been rejected unanimously.
However, since tag excerpts are very visible, minor edits like fixing spelling issues should be encouraged. Furthermore, one cannot comment on tag excerpts. If there is an issue with a post that is too minor for an edit, then you can comment and the OP or someone with edit privileges will fix it. So I think that this should be status-bydesign.