18. A method of operating a system that includes: a processor; memory; the processor being connected for accessing the memory; and string data stored by the memory; the string data comprising two or more data units, each of which can be accessed by the processor; the data units including, for each of a set of two or more acceptable strings of characters, a respective sequence of data units that the processor can access using character data indicating the string's characters; the set of acceptable strings including a first string that is in a first subset of categories, each category in the first subset being one of a set of two or more categories; the first string's sequence of data units including a respective ending subsequence of data units that the processor can access at the end of the first string's sequence; the first string's ending subsequence including: acceptance information indicating that a string at the end of whose respective sequence the processor can access the ending subsequence is one of the set of acceptable strings; and category set information indicating the first subset of categories; the first subset of categories including at least one of the set of categories; the method comprising steps of: operating the processor to access the first string's sequence using first string character data indicating the first string's characters; the step of operating the processor to access the first string's sequence comprising a substep of accessing the first string's ending subsequence; and operating the processor to use the first string's ending subsequence to obtain first string ending data indicating that the first string is one of the acceptable strings and indicating the first subset of categories.
18. A method of operating a system that includes: a processor; memory; the processor being connected for accessing the memory; and string data stored by the memory; the string data comprising two or more data units, each of which can be accessed by the processor; the data units including, for each of a set of two or more acceptable strings of characters, a respective sequence of data units that the processor can access using character data indicating the string's characters; the set of acceptable strings including a first string that is in a first subset of categories, each category in the first subset being one of a set of two or more categories; the first string's sequence of data units including a respective ending subsequence of data units that the processor can access at the end of the first string's sequence; the first string's ending subsequence including: acceptance information indicating that a string at the end of whose respective sequence the processor can access the ending subsequence is one of the set of acceptable strings; and category set information indicating the first subset of categories; the first subset of categories including at least one of the set of categories; the method comprising steps of: operating the processor to access the first string's sequence using first string character data indicating the first string's characters; the step of operating the processor to access the first string's sequence comprising a substep of accessing the first string's ending subsequence; and operating the processor to use the first string's ending subsequence to obtain first string ending data indicating that the first string is one of the acceptable strings and indicating the first subset of categories. 19. The method of claim 18 in which the set of categories includes N categories, the first string ending data being an item of data that includes N bits, each indicating whether the first string is in a respective one of the categories.