Hanging paragraphs vs. warm-up introduction

[jensmaurer]

The ISO Directives, Part 2, require us to get rid of hanging paragraphs.

One sub-issue is that we sometimes have introductory warm-up sentences at the start of a clause or subclause. Occasionally, these are "note"s, making clear their non-normative character. On other occasions (e.g. [constraints.overview]), they are not. Sometimes those warm-up sentences are in a separate subclause "overview", sometimes they form "hanging paragraphs" (often together with normative material).

This issue serves as an anchor to discuss a uniform approach to dealing with these warm-up sentences. Ideas:

• Always put warm-up descriptions into a separate "overview" section (helps avoiding hanging paragraphs).
• Always make warm-up sentences a note.
• Find a differing typographical convention.
• Add warm-up overviews to subclauses which don't have them (yet).

[jensmaurer]

See also #574 and #1730.

[jensmaurer]

Editorial meeting consensus: There are several different situations that warrant different treatment.

• Hanging paragraphs containing substantial normative wording (e.g. Clause 8 [expr]): Reconsider the clause structure in its entirety, move the hanging paragraphs into fresh subclauses, properly structuring the contents. For [expr], have "Properties of expressions" (with more specific subclauses), "Kinds of expressions" (current grammar tree), "Constant expressions".
• Non-normative introductory text as well as (short) normative snippets (e.g. defining a term or similar) should go into a "Preamble" subclause. Use the usual "note" mechanism for non-normative content. (Note: @tkoeppe opposes having a third way of identifying non-normative content (e.g. bars on the side or indentation or similar).) Start a new paragraph once normative content begins. Never mark an entire subclause as "informative".
• Non-normative paraphrase of the contained subclause headings: Delete.
• Having a short paragraph of non-normative introduction before a grammar snippet or a class synopsis is fine. In particular, 23.2.1p1 should be above the synopsis; merge 23.2p1, which also goes before the synopsis; mark as non-normative.

[jensmaurer]

Hanging paragraphs were summarily fixed by addressing an ISO/CS comment on DIS C++20. Keeping open to possibly reconsider the details of the new structure.