The ? character means to match zero or one instance of the previous pattern element; the * character means to match zero or more of the previous element.

字符表示匹配前面模式元素的零个或一个实例，* 字符表示匹配前面元素的零个或多个实例。

youdao

An XML "value," computed by a query expression, may consist of zero, one, or many items, each of which may be an element, an attribute, or a primitive value.

由查询表达式计算出来的XML“值”，可为零项、一项或者多项，而其中每一项可以是一个元素、一个属性或一个原始值。

youdao

Values for array type components can contain zero or one element, and values for set and tree type components can have zero or more elements.

用于数组类型的组件的值可以包含0个或1个元素，用于集合和树类型的组件的值可以包含0到多个元素。

youdao

Right, 'cause that means either I've been handed zero elements which mean there's really no work to be done or I've been handed one element which is a vacuous truth that it's sorted, right?

因为如果给出0个元素,那意味着不需要做任何事,如果给出1个元素，那显然,它是有序的，对吗？

哈佛公开课 - 计算机科学课程节选