Suppress warnings from all non-existing directives/roles

Hi all,

I'm looking for a way to read a reST file with non-standard
directives/roles and suppress its error/warning messages. The ideia is
to not generate error **only** when those non-existing
directives/roles appear, but continue to report errors about other
matters.

To read the file it is used the docutils publish_doctree method. I see
I can use settings_overrides={'report_level':'none'} to suppress all
messages. Can this be done to suppress only that kind of message?
Taking a quick look at the code I tend to say no, but I want to be
sure.

Thanks,
Vinicius

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