This document specifies a reference set of Label Generation Rules (LGR) for the Arabic script for the second level. The starting point for the development of this LGR can be found in the related Root Zone LGR [RZ-LGR-4-Arab]. For details and additional background on the script, see TF-AIDN, "Proposal for Arabic Script Root Zone LGR", Version 3.4, 18 November 2015 [Proposal-Arabic]. Additional work was done by a TF-AIDN group to create extensions appropriate to the second level and these are incorporated in this LGR. (See "Methodology" below). The format of this file follows [RFC 7940].
The document contains certain provisions for customization. (See "Customizing actions for International Reachability" below.)
The repertoire includes the 128 code points for letters used by languages that are actively written in the Arabic script as described in Section 3.2 of [Proposal-Arabic]. For the second level, the repertoire has been augmented with the HYPHEN-MINUS, and three sets of decimal digits:
for a total of 159 repertoire elements.
The repertoire excludes code points for which TF-AIDN was unable to find sufficient evidence of use (see Appendix F in [Proposal-Arabic]). The repertoire is described in Section 3.2 of [Proposal-Arabic] and a subset of [Unicode 6.3].
This LGR does not include combining marks or code point sequences. All combining marks have been excluded for these reasons:
For further details, see Section 3.2, "Code point repertoire included" in [Proposal-Arabic]. (The proposal cited has been adopted for the Arabic script portion of the Root Zone LGR.)
Each code point or range is tagged with the script or scripts that the code point is used with, and one or more references documenting sufficient justification for inclusion in the repertoire, see "References" below. Comments identify the languages using the code point.
Because this LGR contains only a subset of PVALID code points, the Bidi rules expressed in section 2 of RFC 5893 [160] (Bidi Rule) can be simplified to two constraints:
This reference LGR is designed for use in zones shared by more than one script. Where appropriate, cross-script variants have been defined to mutually exclude labels from different scripts that could otherwise be substituted by the users. Once a label has been delegated for one script, any variant labels from other scripts consisting of cross-script variants would be blocked. Any label containing at least one code point that is not a cross-script variant would be considered distinct. Because of that, even large numbers of defined cross-script variants generally do not lead to a high percentage of labels experiencing a collision.
Digit Variants: The two sets of Arabic-specific digits are treated as semantic variants of each other and of the corresponding common (ASCII) digits. By transitivity, they are also semantic variants of any native digits in scripts that also include the common digits. Because of the restriction on leading digits, most labels would contain a unique code point in addition to any digits, thus no variant labels would actually result from any pro-forma cross-script variants. To keep digit variant sets manageable in zones where multiple scripts are present, no attempt has been made at identifying cross-script variants among digits of different numeric value or between a digit in one script and a letter in another, such as between digit zero and Latin letter 'o'.
Variant Disposition: This LGR includes "blocked" and "allocatable" variants, assigned according to Section 4, "Final recommendation of variants for Top Level Domains (TLDs)" in [Proposal-Arabic]. These recommendations balance the desire to minimize the number of possible allocatable variants with the need to keep the definition of variants simple. See also the comments given in the listing.
For the second level, three additional variant types are added: "optionally-allocatable", "activated", and "optionally-activated". They are used to improve user acceptance. The rationale for these new types is provided below.
In generating the variant tables, a number of concepts have been used:
One of the main principles for the stability of the Internet and IDNs is that the end user should be able to reach a website connected to his/her domain name regardless of location. Additionally, an end user reads and types website addresses based on his/her language alphabet and whatever is available in his/her keyboard. Therefore, in order to enforce this principle the input devices (language table) that the user may use to reach a domain name (based on the user location) should be carefully considered when defining variants. Otherwise, it may cause a reachability problem and reduce the user acceptance. For example, if someone registered the domain name “مكة” (all characters from the Arabic language) and a user try to reach the website connected to this domain name from an Internet café or airport, say, in Pakistan. He/she will not be able to reach that website unless if the variant “مکۃ” (Urdu variant) is already allocated and activated. Thus, variants need to be studied from both similarity point of view (by language community) and reachability pointy of view (based on input devices used by other language communities).
Consistency is a very important concept in generating variants. Regardless of the selected applied-for label the list of generated allocatable variants should be the same. As we are dealing with normal users at the SLD, their 1st choice (applied-for) label might not be the one that will be used by the internet community. Therefore, a registry should provide the registrant the ability to "correct" his/her choice if he/she was not successful with the first try. For example, the word “Internet” is written in most Arab countries in North Africa as (أنترنت) while it is written in other Arab countries as (إنترنت), while end users often write it as (انترنت). Therefore, if someone registered "أنترنت", he/she should be able to enable "إنترنت" or "انترنت". Additionally, many words have two correct ways to write them, for example, both "آدم" and "أدم" are widely used for the same name Adam. Hence, if someone registered "أدم" he/she should be able to enable "آدم" or "ادم”. This is achieved by making variants allocatable in at least one direction in the LGR.
Based on the principle expressed in the previous item, some code points are involved in at least one variant mapping of type "activated", "optionally-activated", or "optionally-allocatable. The dispositions related to these mappings may be optionally modified by a registry by editing the appropriate action elements. See the section on "Customizing Actions for International Reachability" for details of how this feature can be made mandatory or disabled.
The specification of variants in this reference LGR follows the guidelines in [RFC 8228].
This proposal defines the following named character classes:
Actions include the default actions for LGRs as well as that needed to invalidate labels with misplaced combining marks. They are marked with ⍟. For a description see [RFC 7940].
The following rules aim at reducing the allocation of redundant labels.
In addition, this LGR includes WLE rules and actions specific to the Arabic script found in Section 5, "Whole Label Evaluation (WLE) rules" in [Proposal-Arabic]. As specified, the rules and actions serve to prevent the mixing of two variants of the same code point within the same label. This reduces overproduction of variant labels. The rules are listed here with the numbers given in Table 17 in [Proposal-Arabic]. See also the comments given for each rule or action. Note that that WLE Rules 1, 2, 3, and 8 part of that Table 17 are omitted here because they are superseded by the rule restricting languages mixing described above.
The three non-default variant mapping types used in this reference LGR trigger actions that result in variant label dispositions as follows:
Variant mappings of type "activated" lead to a disposition of "activated", which implies means the variant label should be allocated. This variant type is used here for the variant mappings between the three sets of digits. Activated variants are handled by the first action above, and are not affected by the optional customizations described below.
As described above, this LGR is designed so that full "international reachability" is optionally available. It can easily be enabled with a small customization.
The disposition for the second of the actions listed above is by default set to "allocatable" which makes the variant available to registrants that would like to support international reachability. Some registry operators may desire to make support for such variants mandatory, in which case the disposition (disp="allocatable" in the XML) for the relevant action could be changed from "allocatable" to "activated" without further changes to the LGR.
The disposition for the last of the actions listed above is by default set to "blocked" which reserves the variants of type "optionally-allocatable". Some registry operators may desire to support such variants as allocatable, in which case the disposition (disp="blocked" in the XML) for the relevant action could be changed from "blocked" to "allocatable" without further changes to the LGR.
Most of the code points involved in labels resulting in "activated" or "allocatable" actions are subject to "no-mix" rules to decrease the number of activated or allocatable variants. This is especially a concern for the "activated" action which results in forced delegation.
If optional variant labels are all made allocatable, a significantly large number of allocatable variant labels can potentially be created. Keeping the allocatable variant labels manageable is advised by SSAC in their [SAC060] report. One way to contain such variant labels, as suggested by the Arabic script community, is to allow only the variant labels which are usable and still block those which may be redundant, e.g. cannot be typed from a single keyboard supporting a given language. For this purpose, the no languages mixing rule is part of this LGR.
Furthermore, applying this customization for variant sets involving code points which do not have "no-mix" should be done with caution. This is especially true for the variant set including the ALEF characters, for which an external policy should be established to ensure that only a strictly limited number of variant labels are allocated. It may not be possible to create a general policy that determine which of the variants from among a potential large variant pool are indeed suitable; therefore, the selection may have to be left as a choice to the registrant, but within a strict cap.
This reference LGR for Arabic script for the 2nd Level has been edited by Michel Suignard and Asmus Freytag, based on extensive community input. This LGR is based on the Root Zone LGR for Arabic and relies on information contained or referenced therein, see [RZ-LGR-4-Arab]. Suitable extensions for the second level have been applied according to the [Guidelines]. The original proposal for an Arabic Script Root Zone LGR [Proposal-Arabic] that this LGR is based on, was developed by the Task Force for Arabic Script IDNs [TF-AIDN]. The specific features related to the International Reachability aspect were drafted by a TF-AIDN sub-group (namely in alphabetical order: Abdalmonem Tharwat Galila, Abdeslam Nasri, Abdulaziz Al-Zoman, Abdulrahman Alghadir, Hazem Hezzah, Nabil Benamar, Raed Alfayez, Tarik Merghani). In addition, Sarmad Hussain provided editorial support.
For more information on methodology and contributors to the underlying Root Zone LGR, see [Proposal-Arabic], as well as [RZ-LGR-Overview].
The following general references are cited in this document:
For references consulted particularly in designing the repertoire for the Arabic script for the second level. please see details in the Table of References below. References [0] to [12] refer to the Unicode Standard versions in which the corresponding code points were initially encoded. References [100] and above correspond to sources justifying the inclusion of the corresponding code points. Entries in the table may have multiple source reference values. References [150] and [160] indicate the source for common rules.
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