can someone suggest how possible to interpret body?
There's no difference in the interpreted Java type of the c:set's body. It are in all cases just String.
Even when you set a non-String type as c:set's body using EL such as
<c:set var="foo">${bean.someInteger}</c:set>
it'll be converted to String anyway by String#valueOf().
Only when you process the variable afterwards, there may be difference, depending on how you processed it. For example,
<c:set var="movieList">One,Two,Three</c:set>
<c:set var="realMovieArray" value="${fn:split(movieList, ',')}" />
will result ${realMovieArray} being a String[] with values of One, Two and Three.
<c:set var="alphabet">A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z</c:set>
<c:forTokens items="${alphabet}" delims="," var="letter">
${letter}
</c:forTokens>