Question

When you enter search keywords in the search box of file explorer and the onedrive option is selected?

Answer 1

When you enter search keywords in the search box of file explorer and the onedrive option is selected, the search will be automatically expanded including the folders which are located in your OneDrive cloud. It's actual for Windows 8, 8.1 and 10. 

Answer 2

The search box which is located at the top right corner of the open window is limited to the selected folder but one can expand the search per user. But when the onedrive options is selected the search is automatically expanded to include every folder on the hard drive.