How to get related list Id

This is very strange that it is not documented anywhere. I took time to research. Here is what I found: For Standard Related Lists like Opportunities or Contacts related lists on Account id of the related list are:

RelatedOpportunityList RelatedContactList RelatedCaseList

For Related lists of custom objects it's the id of the Lookup or Master-detail field to the parent object. So if we have Custom_Object__c with Lookup field Account__c to account we need to go to this field and copy id of that field.

But there is an easier way to find the id: if you open source of the page you will see id of the div element for related list has id like this: parentId + '_' + relatedListId. Couple examples(highlighted related list id): custom object: Standard(opportunity related list on account):