A software feature permitting form fields, etc., to be autocompleted.(noun)
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Use "autocompletion" in a sentence
"· Easy and quick inline username autocompletion in replies and direct messages"
"Will there be any kind of autocompletion / intellisense system integrated in this?"
"Not only does it do this kind of autocompletion, but it also opens a small 'scratch preview' pane showing the function / method signature - i.e., the expected arguments and return value!"