To enable caps lock on the iPhone (which only has one shift), use the 'Enable caps lock' option in Settings/General/Keyboard. Then you can double-tap shift to turn on caps lock.
I basically never use CL on a regular PC, since it's easier to just hold shift while you type the word most of the time. On an iPhone though, it's actually pretty useful at times.
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To enable caps lock on the iPhone (which only has one shift), use the 'Enable caps lock' option in Settings/General/Keyboard. Then you can double-tap shift to turn on caps lock.
I basically never use CL on a regular PC, since it's easier to just hold shift while you type the word most of the time. On an iPhone though, it's actually pretty useful at times.