Current rulesets (except modsecurity) does not make use of the IDMEF Action class.

4.2.6.2.  The Action Class

   The Action class is used to describe any actions taken by the
   analyzer in response to the event. 
   category

      The type of action taken.  The permitted values are shown below.
      The default value is "other".  (See also Section 10.)

   +------+-------------------+----------------------------------------+
   | Rank | Keyword           | Description                            |
   +------+-------------------+----------------------------------------+
   |    0 | block-installed   | A block of some sort was installed to  |
   |      |                   | prevent an attack from reaching its    |
   |      |                   | destination.  The block could be a     |
   |      |                   | port block, address block, etc., or    |
   |      |                   | disabling a user account.              |
   |      |                   |                                        |
   |    1 | notification-sent | A notification message of some sort    |
   |      |                   | was sent out-of-band (via pager,       |
   |      |                   | e-mail, etc.).  Does not include the   |
   |      |                   | transmission of this alert.            |
   |      |                   |                                        |
   |    2 | taken-offline     | A system, computer, or user was taken  |
   |      |                   | offline, as when the computer is shut  |
   |      |                   | down or a user is logged off.          |
   |      |                   |                                        |
   |    3 | other             | Anything not in one of the above       |
   |      |                   | categories.                            |
   +------+-------------------+----------------------------------------+

      The element itself may be empty, or may contain a textual
      description of the action, if the analyzer is able to provide
      additional details.