Few points.. 

In Glossary: We may consider to -

Add:
Alias (In this document, we are calling this as "substitute ASCII address")
Downgrading
LGR
IDN

Change:
Variant characters: "Characters in a script with the same meaning but different visual representations", does not seem to explain correctly. we need to rewrite by considering the following. 

Recommended by Sarmad on 10th April:  
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Please either use “variant label” or “variant code point” to clarify which level you are talking about.  Using “variant” is ambiguous as it can mean either a label or a code point.  This practice is being recommended by the IDN Guidelines WG in their recent revision of the IDN Guidelines.

So that could be visually identical?  - YES variants – though identical is hard to define

Or confusingly similar? – NO, not variants – unless considered variants for some other reason by the community

Or the same semantic meaning? – Yes for Chinese, but could be considered non-variants for other scripts
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IMAP: Internet Message Access Protocol, a standard for managing mail messages and folders on remote servers. The current version is IMAP4. Compare to POP.

The domain name used receive.net / sender.org in examples may require attention as I found that receive.net is resolving to 69.172.201.153 . May be we can have receive.uasg.tech and send.uasg.tech or something else . 

These are the few suggestions before I read it once more. 

Thanks.