-Those attempting to understand these message flows should become familiar with (at the minimum) the [DFRN protocol document](https://github.com/friendica/friendica/blob/master/spec/dfrn2.pdf) and the message passing elements of the OStatus stack (salmon and Pubsubhubbub).
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-Most message passing involves the file include/items.php, which has functions for several feed-related import/export activities.