eBNF 语法中的运算符优先级

问：

我有以下 eBNF 语法：

expression   = term { add_operator term }
term         = factor { mul_operator factor }
factor       = "(" expression ")" | variable | number
add_operator = "+" | "-"
mul_operator = "*" | "/"

variable   = letter { letter | digit | "_" }
letter     = "a" | "b" | ... | "z"

number     = [sign] digit { digit }
digit      = "0" | "1" | ... | "9"
sign       = "-"

为什么我需要因子、项和不同的运算来mul_operator和add_operator。运营商有必要优先吗？如果是，它将如何工作？