15. A system comprising: 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 and use to obtain first string ending data indicating that the first string is one of the acceptable strings and indicating the first subset of categories; 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.
15. A system comprising: 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 and use to obtain first string ending data indicating that the first string is one of the acceptable strings and indicating the first subset of categories; 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. 16. The system of claim 15, further comprising instructions stored by the memory that the processor can execute in using a string's characters to access the string's sequence of data units.