Valuation account

This is a memorandum on valuation account, which I studied yesterday. When we study accounting, we sometimes come accross "valuation account." The easiest topic is "allowance for uncollectible account." Assume that we have a lot of account receivable. It is slightly doubtful to collect all of them, in general. Then, according to thinking of "allowance," we can estimate "net account receivable,"which will be definitely collectible.

There are other accounts classified as valuation account:

• "Deferred gain" in sale-leaseback transaction
• "LIFO reserve" for evaluation of inventory and so on...

I found these were "assets" account, and is it essential for valuation account? In other words, are there any valuation account of "liability?"