A function such as @code{substring} uses both a string and numbers as
arguments. The function returns a part of the string, a substring of
the first argument. This function takes three arguments. Its first
-argument is the string of characters, the second and third arguments are
-numbers that indicate the beginning and end of the substring. The
-numbers are a count of the number of characters (including spaces and
-punctuation) from the beginning of the string.
+argument is the string of characters, the second and third arguments
+are numbers that indicate the beginning (inclusive) and end
+(exclusive) of the substring. The numbers are a count of the number
+of characters (including spaces and punctuation) from the beginning of
+the string. Note that the characters in a string are numbered from
+zero, not one.
@need 800
For example, if you evaluate the following: