What is meant by “bi-directional” in this context? I think you mean “can handle bi-directional domain names”. ASCII characters are inherently Left-to-right and hence never bidirectional. From: ua-eai-bounces@icann.org [mailto:ua-eai-bounces@icann.org] On Behalf Of Don Hollander Sent: Monday, January 23, 2017 11:28 AM To: Mark Svancarek <marksv@microsoft.com>; HEALTH Yao <yaojk@cnnic.cn>; ua-eai@icann.org Cc: ua-coordination@icann.org Subject: Re: [UA-EAI] [Ext] RE: [UA-Coordination] Revised UASG013 - Quick Guide to EAI This is what I have now: Punycode is an algorithm that converts a non-ASCII domain string into an ASCII string. ASCII strings that have gone through the Punycode process can be identified by a prefix of xn--. The Punycode algorithm is bi-directional. See https://tools.ietf.org/html/rfc3492<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Frfc3492&data=02%7C01%7Cstuartst%40exchange.microsoft.com%7C36a667bd28d74362262008d443c5ebde%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636207964727009377&sdata=WjtnPYPKNEpGDJS%2ByeUCwtiIcZrPN0A9Kfi65FJG%2FLs%3D&reserved=0> From: Mark Svancarek <marksv@microsoft.com<mailto:marksv@microsoft.com>> Date: Tuesday, 24 January 2017 at 8:23 AM To: HEALTH Yao <yaojk@cnnic.cn<mailto:yaojk@cnnic.cn>>, Don Hollander <don.hollander@icann.org<mailto:don.hollander@icann.org>>, "ua-eai@icann.org<mailto:ua-eai@icann.org>" <ua-eai@icann.org<mailto:ua-eai@icann.org>> Cc: "ua-coordination@icann.org<mailto:ua-coordination@icann.org>" <ua-coordination@icann.org<mailto:ua-coordination@icann.org>> Subject: [Ext] RE: [UA-EAI] [UA-Coordination] Revised UASG013 - Quick Guide to EAI Good catch. The ACE prefix indicates to a parser that the following string is the Punycoded transformation of an IDNA-compatible Unicode string, but is not actually a part of that transformation. From: ua-eai-bounces@icann.org<mailto:ua-eai-bounces@icann.org> [mailto:ua-eai-bounces@icann.org] On Behalf Of Jiankang Yao Sent: Sunday, January 22, 2017 6:27 PM To: Don Hollander <don.hollander@icann.org<mailto:don.hollander@icann.org>>; ua-eai@icann.org<mailto:ua-eai@icann.org> Cc: ua-coordination@icann.org<mailto:ua-coordination@icann.org> Subject: Re: [UA-EAI] [UA-Coordination] Revised UASG013 - Quick Guide to EAI Hello, The definition "Punycode is an algorithm that converts an IDN into an ASCII string that starts with xn--. The Punycode algorithm is bi-directional. " needs some adjustment. xn--abcdeddaa where "xn--" is a prefix and "abcdeddaa" is output of the Punycode algorithm. So Punycode output does not include "xn--". ======================================following are texts from RFC5890=============================== " the string following "xn--" must be the valid output of the Punycode algorithm and must be convertible into valid U-label form." "An "A-label" is the ASCII-Compatible Encoding (ACE, see Section 2.3.2.5[tools.ietf.org]<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense....>) form of an IDNA-valid string. It must be a complete label: IDNA is defined for labels, not for parts of them and not for complete domain names. This means, by definition, that every A-label will begin with the IDNA ACE prefix, "xn--" (see Section 2.3.2.5[tools.ietf.org]<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense....>), followed by a string that is a valid output of the Punycode algorithm [RFC3492[tools.ietf.org]<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense....>] and hence a maximum of 59 ASCII characters in length. " ________________________________ Jiankang Yao From: Don Hollander<mailto:don.hollander@icann.org> Date: 2017-01-22 17:33 To: ua-eai@icann.org<mailto:ua-eai@icann.org> CC: Tan Tanaka, Dennis<mailto:dtantanaka@verisign.com>; Mark Svancarek via UA-Coordination<mailto:ua-coordination@icann.org>; Dr. AJAY D A T A<mailto:ajay@data.in>; Stuart Stuple<mailto:stuartst@exchange.microsoft.com> Subject: [UA-Coordination] Revised UASG013 - Quick Guide to EAI Last month I sent out a formatted Quick Guide to EAI. This resulted in a number of comments from Ajay, Stuart, Mark, Lars & Dennis. These enhancements were mostly focused on the Email Service Provider. I have revised the source document which is attached. And for reference, I’m also including the formatted earlier draft. Could I please get any final comments by the end of this week (25th)? Thanks. Don Don Hollander Universal Acceptance Steering Group Skype: don_hollander