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.

Also checked (among others):

  • 2
    "Nothing about what parts should be emphasized." Obviously, you emphasise the words you want to stand out. – Kate Bunting Mar 22 at 13:39
  • 1
    What makes you think this is recommended in a style guide? Have you seen it in one that you now forget, because this might help us identify it. Note that the example you post bolds the first line, not the topic sentence. – Stuart F Mar 23 at 10:07

TinfoilHat identified a main-site question about capitalising the first few words in a sentence, and although that asked for the name of the technique, one answer identified a principal proponent as Robert Bringhurst, in his seminal Elements of Typographic Style.

The answer there quoted Bringhurst:

It is common practice to set the first word or phrase after the versal in caps, small caps, or boldface, as a bridge between versal and normal text.

and also included an image of the examples from Elements.

A linked answer on GraphicDesign.SE shows a bit of history; the practice is actually centuries-old.

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