// Normal search request
SearchRequest searchRequest = SearchRequest.of(b -> b
    .size(10)
    .from(10)
    .query(q -> q
        .matchAll(m -> m)
    )
);

// Using it to build Msearch
MsearchRequest msearchRequestOverload = MsearchRequest.of(ms -> ms
    .searches(s -> s
        .header(h -> h.index("index"))
        .body(searchRequest)
    )
);

// Or script source
ScriptSource scriptSourceOverload = ScriptSource.of(s -> s
    .scriptTemplate(searchRequest)
);