Tax line research has always been in the right-click menu for tax form lines, and it's a clunky interface just as rfasset described.
The right click menu also has Master Tax Guide or you can click on the green Tax Research icon in the top bar.
If you click on the green Tax Research icon, you can get to the TPP 1040 Lite tax line research by expanding:
Federal Tax
Federal Tax Editorial Content
CCH Tax Prep Partner
TPP 1040 Lite
and then scroll thru the various subjects. Or click on CCH A-LINE-D and that clunky interface will open in a popup window.