So my Ranger came with a hard tonneau but I have removed it. The bed has no liner. While looking at the bed there seems to be deliberate notches, holes, tie downs, a few stair-step looking things etc. I know what the tie downs are for, as well as the 4 stake holes. All the other indentations seem to have a purpose but I am clueless and I haven't found any diagram or manual that addresses. Any ideas?

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2007 Sport Supercab 3.0, automatic