Comments don't support HTML, merely a small subset of Markdown. See: https://webapps.meta.stackexchange.com/editing-help#comment-formatting (you'll find this by clicking the "help" link under the big Add Comment button).
A while back there was some issue with the wildcard expansion generating excessively long URLs that would be rejected by the web server. Jeff imposed an expansion limit as a workaround, which seems to limit the wildcard matches to the top 20 most popular applicable tags.
This is by design and is a recent change.
The syntax you see inserts the image and creates a link to the image. This way images that are larger than the column for posts can be scaled down in the post but the full version of the image is easily gotten to.
The syntax to do that has been around for a long time, it's just that the image button was recently ...
The decision whether this error is rendered is made on the server when the add comment link is rendered (it has an additional data-reg="true" attribute), since it also depends on other things that would require an additional round-trip to the server each time a user clicks this button - which we don't want.
After you've reached the required rep you need to ...
There are a handful of redundant phrases - including some containing the name of the tag itself - that are not displayed on tags list, to help ensure there's room for the non-redundant parts of the tag excerpt.
The google spreadsheets tag wiki doesn't match any of these, so it's displayed in full.
For details, see: New tags page mangles tag wiki excerpts
There are always some number of rendering inconsistencies between the mobile and desktop versions of Chrome, even if you're not using any beta versions.
That's why we have a mobile version of the site, accessible via the "mobile" link in the footer - I can confirm that the table (while indeed poorly-rendered in the full site on mobile Chrome) appears ...
Your text entry is expected to be mandatory and supplemental (and in my case it's always has been so) to the sentence stub.
The comment box, on the other hand, is optional and hence the placeholder text to guide. I'm not sure I see the reason why the predefined offtopic comment should be changed to placeholder type?
The number appears to be your total StackExchange network reputation rather than your WebApps reputation. Meanwhile, badges are only shown from accounts with more than 200 points. This is similar to the rules for Flair, except since you need a minimum of 20 points to chat I guess it counts them all.
See also this meta SO discussion.
The inbox message relates to this question which was closed as a duplicate of this question.
You asked the initial question (and is actually where the comment is) hence why you get the notification.
I guess SE have implemented some redirection based on the whether the question is closed or not. As this is a duplicate it automagically redirects you to the ...
What seems to have happened is that the suggested edit was looked at - the reviewer decided to improve it but also unselected the checkbox for "this edit was helpful", causing the suggested edit to be rejected, but also for your changes to be incorporated into his edit.