If you have never come across stemming before, you can think of it as being a method in which you can search for a word and have related words returned. Thinking of it more technically, it is a method of producing morphological variants of a root or base word. It can reduce words such as "spraying", "sprayable", "sprayed" or "sprays" to the root word of "spray". This will allow you to search for a base word and not have to additionally include variants of that word in your query.
This is a more selective form of stemming. If you only want certain words to be stemmed, you can add an asterisk at the end of the word you want to be stemmed.
There are two wildcards, the question mark ? and the asterisk *. Wildcards can only be used in the middle or at the end of the word. One ? represents one character, the * represents an unlimited number of characters, i.e.:
car? (will give you cars, card, care…)
car* (will give you car, carton, carbon, cardio…)
Much like Google and Bing, CAS Scientific Patent Explorer will search up to 1500 wildcard variations per query. The limit is in place to ensure that you only get the most relevant search results returned.