[Question] Is constraint f(e) = true really necessary for max_right?

[KeiichiHirobe]

Doc of max_right/max_left in segtree/lazy_segtree says as below.

https://github.com/atcoder/ac-library/blob/master/document_en/segtree.md?plain=1#L135 https://github.com/atcoder/ac-library/blob/master/document_en/lazysegtree.md?plain=1#L145

But, as far as I read source code, max_right/max_left doesn't need Constraint f(e) = true.(Maybe I'm missing something) Why does max_right/max_left need this constrint?