Any items that are added to Squirro go through the Squirro Pipeline (see also Architecture). In that Pipeline the items are normalized and enriched, before they are written into the index. This process is called Data Enrichment and is highly configurable.
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The Built-in enrichments and the Pipelets can be configured for individual sources. This is done with the processing config, which can be provided when creating or updating subscriptions (see the Subscriptions resource).