Some symbols cannot be registered

[ishanijerin1]

When registering excluded keywords, symbols such as ", ! @ % ^ () = {} ; ~ ` <> ? \ |." cannot be registered.
Additionally, device-dependent characters cannot be registered either.

Site operators (site:～) and search operators (OR) are ignored.
The excluded keywords will be treated as if they did not contain site operators or search operators (such as or or and).

For example, excluding the keyword "ad agency" which contains the site operator is the same as excluding the keyword "ad agency".

I don't think most people would include site or search operators in their excluded keywords, but it's still good to be aware of this.

Exclusion keywords may not work if the search is for a phrase that is 17 words or more (Yahoo! 11 words or more).
According to the official Google help, "If a user searches for a phrase consisting of 17 or more words and uses the same word as an excluded keyword for the 17th or subsequent words, your ad may still be displayed." (Yahoo is 11 words.)

Your ad may also appear if someone searches for a phrase that has 16 or more words and uses the same word or words as your negative keyword any word after the 17th word.

About negative keywords – Google Ads Help
You can enter up to 10 negative keywords per line. If you enter more than 11 words, an error will occur. Please make sure that the negative keywords you are adding some of the important considerations are 10 words or less per line.

About excluded keywords – Help – Yahoo! Ads
This is a rare phenomenon as keywords are generally kept concise to 10 words or less, but if they are still displayed even though you have registered an excluded keyword, it may be a good idea to be aware that this could be one of the causes.

Should I exclude research queries like "what is..." or negative words like "cancel"?
One of the queries that are difficult to determine keywords for is a search query such as "What is ~" or a negative word such as "XXXX cancellation".
In conclusion, you should not exclude them. However, there are some patterns that should be excluded.