They didn't even have mentioned the comments in the source code
/// Mommy intentionally lets her little ones call her recursively, since they might want to hear more from her~
///
/// If they call her a thousand times in a row, though, something has probably gone wrong π
const RECURSION_LIMIT: u8 = 100;
/// This name is intentionally not user-configurable. Mommy can't let the little ones make *too*
/// much of a mess~
const RECURSION_LIMIT_VAR: &str = "CARGO_MOMMY_RECURSION_LIMIT";