[chef] Significance of attributes in metadata.rb file

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I read http://docs.opscode.com/essentials_cookbook_metadata.html, but it's not
clear.

I see mysql cookbook's metadata.rb doesn't include all attributes used by that
cookbook (ex: grants_path is not there).

So my question is - when and where is the attribute list included in
metadata.rb used? Can I rely on that list for any purpose?

Thanks Rags