Sentence:  No fold could <WSD>be</WSD> accidental , each turn of the drapery had to serve organically , to cover the Madonna 's slender legs and feet so that they would give substantive support to Christ 's body , to intensify her inner turmoil . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)