Edit summaries are not always straightforward! They may contain piped links or numeric HTML entities. When I make a change to complex code involving links, I sometimes try to reproduce my change to the wikitext in the edit summary by inserting a zero-width space between two consecutive instances of the square bracket ([) so that they do not actually create a link. I need a way of checking that I’ve done it right. Anyhow, as errors in published edit summaries cannot be corrected, I always have previewed my edit summaries before publishing.
Topic on Talk:Talk pages project/Replying/Flow
"Advanced" button does that I guess ~~~~
Not in any way that I can see. "Advanced" allows me to formulate the edit summary but not to preview it.
No, it’s not currently possible. See the Phabricator ticket I linked above about Whatamidoing (WMF)’s request (you may want to create a Phabricator account using your Wikimedia account and subscribe to the task to be alerted when the developers start working on it).
As a workaround, if you're in the wikitext source mode, you could paste your edit summary into the main editing box (on a separate line) and see what the live preview says. Then remove it from your comment before you post.
I don't know if this request will get implemented this year.
There are differences in how wikitext works in summaries and in the reply text itself (e.g. templates are not expanded, no bold, italic etc. markup, C-style /* comments */ create section links, and so on), so this workaround provides only an approximation.
True.