| `\`| 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. |

| `\`| 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。|