by default the word is optional, use above operator to modify your request:
- A leading plus sign ('+') indicates that this word must be present.
- A leading minus sign ('-') indicates that this word must be exlude.
- Enclosed within double quote ('"') to search for the exact word or phrase.
- The asterisk ('*') serves as the truncation or wildcard. It should be appended to the word to be affected.
- A leading tilde ('~') mark "noise" words but don't reject it.
- These two operators ('<' or '>') are used to change a word's contribution to the relevance value. The > operator increases the contribution and the < operator decreases it.