Hi Jason Feng,
Thank you for reporting this issue.
I can confirm that you observations are indeed correct and the AutoComplete's highlightFirst option is documented with a default value of "true" in the API Documentation. The default value, however, is indeed set to `false` for the AutoComplete.
The issue is now logged as a bug in the Kendo UI Core repository and we will prioritize it according to its severity.Taking this into consideration, I would suggest setting the option to `true` in the mean time in order to enable the functionality.
As a token of gratitude for helping us discover this issue, I have also updated your Telerik Points accordingly.
Regards,
Dimitar
Progress Telerik