对于和本文类似的用例，该参数是不可选的 —这至关重要！

For a use case like the one in this article, this parameter is not optional—it is critical!

youdao

可以在xsl：param元素中指定参数是可选或必须的，除非该元素是xsl：function的子元素，这种情况下参数是不可少的。

You can designate parameters as optional or required in the XSL: param element, except when that element is a child of XSL: function, in which case they are always required.

youdao

可以在xsl：param元素中指定参数是可选或必须的，除非该元素是xsl：function的子元素，这种情况下参数是不可少的。

You can designate parameters as optional or required in the XSL: param element, except when that element is a child of XSL: function, in which case they are always required.

youdao