The Output directive selects filters that will process outgoing response data generated by the Service step. The Output directive allows you to invoke the insert-filter SAF to install filters that process outgoing data. All Output directives are executed when the server or a plug-in first attempts to write entity body data from the client.
The Output directives are executed at most once per request.
You can define the appropriate position of a specific filter within the filter stack. For example, filters that translate content from XML to HTML are placed higher in the filter stack than filters that compress data for transmission. You can use the filter_create function to define the filter's position in the filter stack, init-filter-order to override the defined position.
When two or more filters are defined to occupy the same position in the filter stack, filters that were inserted later will appear higher than filters that were inserted earlier. That is, the order of Input fn="insert-filter" and Output fn="insert-filter" directives in obj.conf becomes important.
For more information, see Chapter 4, Creating Custom Filters.