Mainstream is a synonym of Usual. Usual is a synonym of Common. Common is a different concept from Occasional. 
Shelf is part of Closet. you are likely to find Safe in/at/on Closet. Safe is related to Area. Corner is a type of Area. 
Mainstream <--Synonym--> Usual <--Synonym--> Common <--DistinctFrom--> Occasional 
Shelf --PartOf--> Closet <--AtLocation-- Safe <--RelatedTo--> Area <--IsA-- Corner 