- If FIRST_COLUMN is nonzero, then it should be the 1-based
- column number of the first character in INPUT, used in error
- messages. */
+ If FIRST_COLUMN and LAST_COLUMN are nonzero, then they should
+ be the 1-based column number of the first and
+ one-past-the-last-character in INPUT, for use in error
+ messages. (LAST_COLUMN cannot always be calculated from
+ FIRST_COLUMN plus the length of the input because of the
+ possibility of escaped quotes in strings, etc.) */