I noticed that it's not possible to format text (i.e. apply bold and italics) in custom edit rejection reasons. But there are some canned rejection reasons that contain formatted text.
For example, I used the "irrelevant tags" rejection reason here, and that canned reason has italicized text.
But over here, a user attempted to bold a word in a custom rejection reason by using Markdown formatting, but it showed up as plain text.
As a test, I decided to see if HTML tags would format text, but it didn't work.
Why do custom rejection reasons have to use plain text only? Why can't we format text when typing a custom rejection reason? It seems to me that this is explicitly prohibited, since there are several canned rejection reasons that do make use of text formatting.