However , parentheses are also used to create subexpressions and possibly capture them for later use , something that is covered in the section on backreferences 但是，括号也用于创建子表达式，并可能捕获它们以供以后使用，这一点在有关反向引用的那一节讲述。
And up are considered backreferences if there is a backreference corresponding to that number ; otherwise , they are interpreted as octal codes unless the starting digits are 8 or 9 , in which case they are treated as literal " 8 " and " 9 " 和更高位表达式在具有与该号码对应的反向引用时被视作反向引用；否则，它们会被解释为八进制代码（除非起始位是8或9 ，在这种情况下它们被视为原义的“ 8 ”和“ 9 ” ） 。
