The structure of a CSV type event is expressed by the item name in column elements of the event type definition.
An item expression specifies the location of elements in a CSV type event using the item name.
The format used by item expressions is shown below.
Is specified in a search expression when all items are search targets.
Note
Use "$_" only when a pattern is specified in a search expression. At any other time, using "$_" will return items with an underscore ("_") as the item name.
