Suggest underlines for web. Indicators for off-site? Avoid words that are just links, app or otherwise, without some indication they are functional. Also notes about files when not something viewable directly and size (e.g. 235 kb PDF)

This is all good for web, but what about apps. How DO you tell if something is clickable? I see failures all the time in desktop apps even. So what indicates unless icons or buttons (or underlines) are used?

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