Ash.Filter.Runtime.filter_matches

You're seeing just the function filter_matches, go back to Ash.Filter.Runtime module for more information.
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filter_matches(api, records, filter, loaded? \\ false)

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Removes any records that don't match the filter. Automatically loads if necessary. If there are any ambigious terms in the filter (e.g things that could only be determined by data layer), it is assumed that they are not matches.