In explorer, the bottom portion of an explorer window changed names late in the development cycle of Windows Vista. It was called the "preview pane" for the longest time. The old name snuck into our property naming and our APIs.
Later, the name was changed changed to "details pane". We were able to update most APIs, but the property names were set in stone. Confusingly (to those of us who spoke the old name for a year), the right-hand pane that renders the document is now called the "preview pane".
So now you know the story of why PKEY_PropList_PreviewTitle and PKEY_PropList_PreviewDetails control the behavior of the details pane.
The Details Pane (née The Preview Pane)