The %FinderSelection% token returns (v10.0+) the path of the currently selected file in the Finder. If there is none or more than one file selected, then it returns the empty string.
The %FinderSelections% token returns (v10.0+) the paths of the currently selected file in the Finder, one per line.
Prior to v11, if the selection was an alias/link, this token would return the target of the link. As of v11.0+, the token returns the alias/link.