Has anyone successfully used HasChildren=True/False in a cube view member filter?

I'm building a cube view where I want to pull, in tree view, all descendants of a particular hierarchy but I also want to apply 2 where clauses:  Where the member is either a 'parent' OR where the member's description begins with certain letters.

So my MF looks like this:  U4#MyHierarchy.TreeDescendantsInclusive.Where((HasChildren=True) or (Description Startswith FS)).

To step back though, at this point, I can't even get the first part of that syntax to work on its own.  I keep getting unexpected text "HasChildren.....".  Doesn't seem to matter how I write this (with or without the 'where') per the OS documentation.

I'm just wondering if anyone has successfully used this and perhaps provide a working example so I can figure out what I'm doing wrong here.

Thanks in advance for any guidance.