Not too long ago, while teaching CDA to a group of students, I came up with a new way to explain moodCode in HL7 Version 3 and CDA.
Mood describes the steps within a workflow.
DEF - This step provides a definition a workflow task to be performed.
INT - This step indicates that a workflow task is to be performed in the future.
RQO/ARQ - This step is an order (or a request) to perform a specific process (or encounter).
PRMS/APT - This step is a commitment to perform the process (or encounter).
EVN - This step is to documents the performance of the process or encounter.
Each of these "moods" represents a different stage of negotiation in the overall workflow.
There's no discussion of the relationship to linguistic moods, et cetera. Perhaps we could call this something like processingStateCode or workflowStateCode in future versions of Version 3 (although given the challenges of momentum, that might not fly).