目前可以用的部分：

+ (plus) = document must include this word.
- (minus) = document must not include this word.
When a + or - is not specified, the query engine uses an algorithm to match
the words to the text.

暂时未实现的部分：

Terms within quotes are assumed to be a phrase. (
Wildcards
* ? (question mark) = represents a single character
* * (asterisk) = represents any number of arbitrary characters

不允许的部分：

Boolean operators (AND, OR, NOT) are not valid and are ignored.
Parentheses in the basic syntax are not supported.