Review and refine ancil_2anc documentation

📚 Documentation Request

At present, understanding the capabilities of `ancil_2anc` requires going to multiple sources of information. We should review and refine both the docstrings and help so that it is standalone and not in need of supplemental materials/documentation.

Start by locating the ancil_2anc entry point and reviewing its current docstrings and help output. Compare the information available there with any supplemental documentation currently needed. Done means the capabilities and usage are understandable from the docstrings and help alone.

Written by the indexing model from the issue text.