A quick diagram I drew up to help me remember how Enterprise Library’s logging configuration file routes messages using filters, categories and severity.
The priority filters and logging enabled filters are set within the LogFilters node and are the first level of filtering applied to log-messages.
The category assigned to a message is then used to determine which listeners/sinks are written to via the categorySources node. At the category level, the switchValue is used to log on those messages with a Severity level set to that level and above. (All logs all severity messages).