unrecognized actiontype in maction

Hello everyone!

While working on my summer project with MathML maction, there was
discovered an uncertainty in the REC. In section
3.7.1.1<http://www.w3.org/TR/MathML3/chapter3.html#id.3.7.1.1>it says:

By default, MathML applications that do not recognize the specified
> actiontype should render the selected sub-expression as defined below.
>

and then it goes on to describe the actiontype attribute and the effect of
the selection attribute.

The question is, how to deal with the selection attribute when we get an
unrecognized actiontype? Should the selection attribute on maction be
considered by default?

-- 
Andrii Zui