Hi!
This feature can save lot of time. Now almost all search engines have auto-complete feature which is saving lot of time when you search any topic and makes your work easier. Imagine this on was on your Mac? You will save even more time when you will be typing many pages or writing article for your blog. This is very simple feature. Just press Command + Period (or full stop) on your Mac. This will show possible words which you can use while typing.
When you start typing any word, just press Command + Period and a list will appear and from that list you can select the word to complete your sentence. This feature can be used to skip long letters. You can write some characters and hit Command + Period. From the list popped-up, you can scroll down and up with arrow keys and select the work with return/enter key.
Unfortunately this auto-complete feature doesn’t quite work like Google Search Box. Suppose you bring up the menu and if you start typing again the menu will hide. But this feature might get improved in new version of OS. If you auto-complete same words again and again they will appear at the top of the list. This will allow you to save those few seconds. 
and this auto-complete feature don’t work everywhere. You should keep trying on other apps. Some of them might not support in feature so don’t get shocked!
