spu_promote((unsigned int)5, 1) creates a vector of unsigned ints with 5 in the second element (element 1), and the remaining elements undefined.
spu_promote((unsigned int)5, 1) 创建了一个 unsigned int 类型的向量，其中第二个元素（元素 1）为 5，其他元素尚未定义。
PT_NULL the array element is unused; other members' values are undefined. This type lets the program header table have ignored (whole) entries.
NULL该类型程序头表表项未使用；该表项其他的成员值都是未定义的。这种类型让程序头表忽略程序头表项。
In CSS 2.1, if the inline element is split across multiple lines, the containing block is undefined.
在CSS2.1中，假如行内元素被拆分成很多行，那么包含块是undefined。
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