rule of thumb for highlighting
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helpful rule of thumb is that each layer of highlighting should include no more than 10–20 percent of the previous layer. If you save a series of excerpts from a book amounting to five hundred words, the bolded second layer should include no more than one hundred words, and highlighted third layer no more than twenty. This isn’t an exact science, but if you find yourself highlighting everything, this rule should give you pause.
Link:: Building a Second Brain Book
Полезная эвристика из progressive summarization