The unit is a passage because the engine quotes a span of text and discards the rest of the page, and on at least one surface you can see exactly which span. The largest passage-level dataset published is a year-long vendor study of 15,699,298 Google AI Mode citations across 148 industries, resolving to 4.6 million unique highlighted passages across 2.7 million pages, published in July 2026. Vendor-published; described rather than linked, per this curriculum's sourcing rule.7
Its numbers describe what a quoted passage looks like. 47.7% of citations were scroll-to-text highlights rather than plain links, meaning the engine pointed at a specific paragraph. The median highlighted passage was 117 words. 80% put the answer in the first sentence, about 85% were fully self-contained, meaning understandable without the surrounding page, and 48% of repeatedly-cited passages opened with an explicit question against 22% of one-off passages. The same dataset also shows ranking still governing the whole thing: pages supplying 21 or more highlighted passages had a median organic rank of 1, and among passages reused 100 or more times, 76% came from pages ranking first.
The editing consequence does not depend on trusting those percentages. Write each section so it survives being lifted out with no surrounding context, because that is the only form in which it will be used: a question-shaped heading, the answer in the first sentence beneath it, every qualifier baked into the sentence rather than the paragraph above. Openers like “this means” are structurally unquotable.