[5.2 Font Style Matching, step 7](https://drafts.csswg.org/css-fonts/#font-style-matching) explains that system font fallback is to be performed on a per character basis. Is there consensus for clarifying system font fallback by specifying that system font fallback should/(must?) not be performed for trying to find a glyph for codepoints in the [Unicode Private Use Area and the supplemental Private Use Areas](http://www.unicode.org/versions/Unicode10.0.0/ch23.pdf#G19184)?