While there's a lot of use from the mktoActive and mktoAddByDefault attributes when defining modules for email templates, there's a more common problem that hasn't been addressed with template attributes: requiring a module to be on all emails within a template. Sometimes, it doesn't make sense to include a header/footer/etc. outside of .mktoContainer, so Marketo users may be stuck with trusting that other users will keep modules within an email for compliance reasons--think a module that has boilerplate legal text or subscription information.
In a case like that, you'd want that module to always be in the email, so the ability to do something like mktoRequired="true" in conjunction with mktoAddByDefault would address this problem. This gets even more powerful if order is respected, so, if you have a header module, middle module, and footer module all set to be required, you could allow content to go between header and middle or middle and footer to force brand guidelines.
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