|`\`| Marks the next character as either a special character, or a literal character, or a backward reference, or an octal escape character. For example,`n` Matches the character`n`.`\n` matches newline characters. The sequence`\\` Matches the`'\'` character, while`\(` matches the`'('` character.|

|`^`| Matches the beginning of the input string, unless it is used in a square bracket expression, at which point it indicates that the set of characters is not accepted.|

|`{`| Marks the beginning of a qualifier expression.|

|`\`| Indicates a choice between the two.|

|`\|`| Indicates a choice between the two.|

|`\`| 将下一个字符标记为或特殊字符、或原义字符、或向后引用、或八进制转义符。例如，`n` 匹配字符`n`。`\n` 匹配换行符。序列`\\` 匹配`'\'` 字符，而`\(` 则匹配`'('` 字符。|

|`^`| 匹配输入字符串的开始位置，除非在方括号表达式中使用，此时它表示不接受该字符集合。|

|`{`| 标记限定符表达式的开始。|

|`\`| 指明两项之间的一个选择。|

|`\|`| 指明两项之间的一个选择。|