A reference is always a good starting point. It does let people be on common ground. For example
https://school.stockcharts.com/doku.php?id=technical_indicators:money_flow_index_mfiYou probably want to read the documentation about line delaying and stage-1, stage-2 operations.
Docs - Platform ConceptsWhat some people would call a "canonical" implementation can be found here ... (which you probably can better grasp after seeing the Stage-1 explanation about operators)
https://www.backtrader.com/blog/2019-07-08-canonical-or-not/canonical-or-not/