I would suspect that instead of word frequency, they likely use TF-IDF (or even better, BM25[1]) or LDA [2] to identify relevant keywords to highlight. 1. http

I would suspect that instead of word frequency, they likely use TF-IDF (or even better, BM25[1]) or LDA [2] to identify relevant keywords to highlight. 1. https://en.wikipedia.org/wiki/Okapi_BM25 https://en.wikipedia.org/wiki/Okapi_BM25 2. https://en.wikipedia.org/wiki/Latent_Dirichlet_allocation https://en.wikipedia.org/wiki/Latent_Dirichlet_allocation