In the New Yorker, John McPhee writes about how he creates the structures for his writing. The middle of the piece also contains a description of the text-editor that McPhee uses, along with custom programs coded for McPhee by Howard J. Strauss:

When I met him [Howard Strauss] in 1984, the first thing he said to me was “Tell me what you do.”

He listened to the whole process from pocket notebooks to coded slices of paper, then mentioned a text editor called Kedit, citing its exceptional capabilities in sorting. Kedit (pronounced “kay-edit”), a product of the Mansfield Software Group, is the only text editor I have ever used. I have never used a word processor. Kedit did not paginate, italicize, approve of spelling, or screw around with headers, WYSIWYGs, thesauruses, dictionaries, footnotes, or Sanskrit fonts. Instead, Howard wrote programs to run with Kedit in imitation of the way I had gone about things for two and a half decades.

… Howard thought the computer should be adapted to the individual and not the other way around. One size fits one. The programs he wrote for me ere molded like clay to my requirements—an appealing approach to anything called an editor.

There is more of interest in the whole essay, which is unfortunately behind a paywall.