If SUBSTRING is omitted, the COLUMN parameter indicates the beginning of the text to update.
If SUBSTRING is specified, scanning starts from the position defined by the explicit or default value of the COLUMN parameter.
If SUBSTRING is specified and the scan for it failed, the current line is not updated.
To replace multiple occurrences of the specified text in the current line, first use SCAN to locate the beginning of the specified occurrence of the replaced text. Then use UPDATE with COLUMN=*, which sets the column position to the position referred to by the last SCAN.
