瑜伽論記 7.172

7.172

後二難了故別解，上下想者：謂觀察此身如其所住如其所願等者，如其所願隨觀上下安住其心，故云如其所住觀上觀下。

The latter two are difficult to understand, so they are explained separately. The ideation of above and below means: regarding "observing this body according to how it stands, according to how one wishes, etc.": according to how one wishes, one observes above and below accordingly and fixes the mind; therefore it says: according to how it stands, observing above and observing below.