Hello, Currently the Explanation class has a toHtml and toString method, but it doesn't seem to have any method to output the explanation as a NamedList. Part of the reason is that NamedList is a Solr only concept and it cannot exist in lucene. But this leads to utility functions like (https://github.com/apache/lucene-solr/blob/1d85cd783863f75cea133fb9c452302214165a4d/solr/core/src/java/org/apache/solr/response/transform/ExplainAugmenterFactory.java#L115 and https://github.com/apache/lucene-solr/blob/1d85cd783863f75cea133fb9c452302214165a4d/solr/core/src/java/org/apache/solr/util/SolrPluginUtils.java#L400-L466
which assume a particular structure about explanations. Explanation should instead have a toMap method which returns a Map of key-value pairs which can then be converted to a NamedList in Solr. This can be exceptionally useful if we have a class inheriting from Explanation that adds more attributes. For example for Learning to Rank model explanations we can have a ModelExplanation class which adds doc-specific feature scores and other machine learning model explanations to the output. It also allows the ExplainAugmenter and other classes to have a more generic way of getting an Explanation's data in a structured format. The way it currently does so is very ugly - https://github.com/apache/lucene-solr/blob/1d85cd783863f75cea133fb9c452302214165a4d/solr/core/src/java/org/apache/solr/response/transform/ExplainAugmenterFactory.java#L115 Just wanted to discuss this on the mailing list before creating Jira tickets. Thanks, Sam
