how does iPhone touchscreen work?

Does anyone know how the iPhone's touchscreen works? Also, is it dual touch (only) or multi-touch? I understand it does not work with a stylus or even
fingernail. Is it a segmented resistive sensor, or based on 'frustrated' total internal reflection (like fingerprint sensor), capacitive..??
Kevin
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It is multi-touch; some of the user interface features rely on this.
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