Comment by dredmorbius

Technical / government docs often feature such numbering schemes. I believe part of the history is that those documents were often composed in segments or sections, often by independent teams, such that a fixed page enumeration wasn't readily available and/or would change frequently.

There's a pre-digital publishing trend of loose-leaf or removeable bindings, with publications prepared in sections or with periodic supplements, which began in the late 19th / early 20th century. Those would typically be organised and numbered by section. The concept is somewhat trite now, but I think of it as a significant stage and evolution of publishing, somewhere between fixed-format codices, periodicals, and eventually databases and wikis.