How does iBooks implements its highlight text feature?

I would like to do something similar for an HTML d开发者_Go百科ocument or PDF. How should I go about implementing this feature?

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For an html document, I'd look into doing some simple javascript/css coding.

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Try FastPDFKit, you can perform search and results will be highlighted.

http://mobfarm.eu/fastpdfkit

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iBook uses JavaScript to get the selected text and it uses Images to show highlighted portion.