I'm not exactly sure what you are actually asking about. You are asking about indexes but perhaps are really wanting to create a "Table of Contents". Neither of these features are going to merge the first and last paragraphs of a range into a single line item so they dynamically update but something will be possible if we could understand what it is you actually want.

To be clear on the terminology, perhaps you should attach a sample document that contains the elements you want to 'index' so we can see what you have and what you are trying to get to.

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Andrew Lockton
Chrysalis Design, Melbourne Australia