The distinction is that they apply just to universal-character-names, and _ is not in class XID_Start, but is in non-digit. 

On Tue, May 26, 2020, 17:04 Corentin Jabot <> wrote:
With the exception of underscore, 
Non digit is a subset of xid_start.

digit + non digit is a subset of xid_continue.

Should that be simplified?

On Tue, May 26, 2020, 22:53 Steve Downey via SG16 <> wrote:
Find attached a draft of the UAX31 paper for discussion. 
Viewable at
Source at

(note that github doesn't format the same way that mpark's WG21 format does)
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