See this webpage/demo.
I've seen this "technique"(?) being applied both in print and online.
I want to know if there's a specific style or guide that recommends it, or if it's just common practice.
- It mentions that boldface is one of the methods to add emphasis. Nothing about what parts should be emphasized.
- "In a print context, follow these best-practice ideas"
- It doesn't talk about topic sentences specifically and does not mention who has set/recommended these "best practices".
- Simply suggest emphasizing the first line (as opposed to sentence) of each section.
- No mention of boldface or emphasis.
Also checked (among others):