I am trying to locate the "inventory" tab in the product form with no success. Could not find it in product_template_only_form_view and inherited.
Please note that I don't wan't to replace it but just inherit and add some fields.

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Thanks for the answer. It can be also done by targeting the page in the product form:

<xpath expr="//page[2]//group[1]" position="after">

In the example above page[2] stands for Inventory(it is the second page on the product form).