A very basic question about notations of function spaces that makes me confused

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Assume we have a function space $V$ such that for any function $f$ in $V$ the mapping is $f: X \to R$, and a subdomain $Y \subset X$ for the restriction of the function, say, $f|_Y: Y \to R$ in the restricted function space $V|_Y$. Then, can we say $V \subset V|_Y$ or $V|_Y \subset V$?