Functionally, they work a lot like folders, except that messages can be tagged with more than one label.

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With email and documents you need to manually structure your work content, i.e copy them into the right folders, forward emails of importance to the rest of your team or CC everyone to cobble together collaboration for actionable items.

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Amazingly, the 70, 000 non-work emails I have accumulated over the last 20 years were filed into folders.

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This broad metaphor also lent itself to sub-metaphors, including object-icons such as a rubbish bin (also the work of Mr Mercer when he worked at Apple in the 1980s), folders and files.

ECONOMIST: Metaphorically speaking