Took me too long to realize this wasn't a tool to search for marginalia in scanned manuscripts.
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Some fun context, I was trying to find a scanned copy of the first 'correct' book on optics (written by https://en.wikipedia.org/wiki/Ibn_al-Haytham). Possibly the first person to really use the scientific method in circa 1000CE (!!). And I found this (https://cudl.lib.cam.ac.uk/view/MS-PETERHOUSE-00209/103) filled with interesting optical diagrams like something out of my high school physics notebooks. Anyway - I was also thinking about how they might index interesting doodles in the margins. So it was on my mind.