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?

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

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

http://mobfarm.eu/fastpdfkit

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