There are now quite a few shipped core plugins at LS 4, see https://github.com/LimeSurvey/LimeSurvey/tree/master/application/core/plugins

Some of them only add manir features like https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/PasswordRequirement/PasswordRequirement.php but others are far more complex like https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/expressionFixedDbVar/expressionFixedDbVar.php.

Problem is that only very few (I think https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/customToken/README.md is actually the only one) come with a readme file to explain the technical details, options and include some examples. others only come with avery short description like "Add some function in ExpressionScript Engine to get count from other responses" (https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/statFunctions/statFunctions.php#L23). The common users does not really know what this actually means or how it can be used.

So can we please have a readme fle for these core plugins similar to https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/customToken/README.md ?
There are so many great plugins like https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/expressionFixedDbVar/expressionFixedDbVar.php or https://github.com/LimeSurvey/LimeSurvey/blob/master/application/core/plugins/expressionQuestionForAll/expressionQuestionForAll.php but even I as a long term Limesurvey user do not really know how to use them.
Later on I think we should also link to the readme file from within the plugin manager if possible (or even better load the readme there if exists).