In April 1994, I started to program Mew. Since there were references, inc and scan not to wait the exit, dynamic window configuration, marks, and message cache were implemented in early time.
To tell the truth, Mew displayed MIME messages in MIME mode. When you type `SPC' on a multipart MIME message, Mew moved from Summary mode to MIME mode. Utashiro said to me, however, "Why MIME mode? Summary mode is enough, isn't it?". It's a really breakthrough.
At this time, big problems were how to refile messages and to compose complex MIME.
It is certain that if users are always forced to write Lisp, message refile becomes easy. But I really hate to require users to setup Lisp by themselves. "It is ridiculous to try to choose default refile-folder from message header since there are thousands of candidates. Rather, it is quite reasonable to select the default from existing folder". When this idea hit my head, I could not wait for the next morning. After that, refile feature was enhanced by Nomura.
How to compose complicated MIME message with easy operations? It is a tragedy for users to be compelled to learn a composition grammar. I really wanted to provide simple yet comprehensive method to users. It was Youki that gave me the answer. Yes, MIME is file structure! We can consider that a singlepart is a file while a multipart is a directory. Users can create a file tree without any troubles, of course, and it is a Mew's job to convert the file structure to MIME format.