Unlike the wiki, there are no “raw” files to edit in your capsule. Thus, if you use “e” on an existing file, all the Gemini markup is lost. The solution is to “view source” before you edit: use “.” to view the source, then hit “e” to edit it, remove the first line that mentions the MIME type, and make your edits. Save using “C-c C-c”. When you revisit the page you edited, make sure to reload it using “r” as Elpher caches all your pages.