How do multifocal IOLs work?

I recently had cataract surgery, and got a Tecnis Multifocal 2.75 lens in one eye.

I don't understand how multifocal lenses work. If I understand properly, they allow vision to be clear at every distance. But how is it possible for the vision to be clear at every distance?

 

Artificial intraocular lenses (IOLs) are made of soft, flexible plastic and are used to replace your body’s natural lens. They can also be used to correct pre-existing refractive errors, such as short-sightedness, long-sightedness and/or astigmatism (blurry vision due to an abnormally shaped cornea or lens).

There are a number of replacement lens options available – the lens you choose will influence whether you still require glasses for certain activities following surgery. Multifocal lenses allow clear focus at more than one distance but have a higher risk of visual side-effects (e.g. glare and halos around lights).

• Bifocal lenses allow clear focus at two distances (near/reading and far), but glasses are likely to be required for intermediate distances (e.g. computer work).
  
  
• Trifocal lenses allow clear vision at three distances (near/reading, intermediate and far). Glasses are often not required for standard day-to-day activities following surgery.