source: draft-ietf-iri-3987bis/draft-ietf-iri-bidi-guidelines.xml @ 147

Last change on this file since 147 was 147, checked in by duerst@…, 7 years ago

added Appendix A: List of ASCII Symbols and their Bidirectional Character Types. This is purely informational.

File size: 31.1 KB
Line 
1<?xml version="1.0"?>
2<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
3<!ENTITY rfc2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
4<!ENTITY rfc3490 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3490.xml">
5<!ENTITY rfc3987 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3987.xml">
6<!ENTITY DRAFT "draft-ietf-iri-bidi-guidelines-03">
7<!ENTITY YEAR "2012">
8]>
9<?rfc strict='yes'?>
10
11<?xml-stylesheet type='text/css' href='rfc2629.css' ?>
12<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
13<?rfc symrefs='yes'?>
14<?rfc sortrefs='yes'?>
15<?rfc iprnotified="no" ?>
16<?rfc toc='yes'?>
17<?rfc compact='yes'?>
18<?rfc subcompact='no'?>
19<rfc ipr="pre5378Trust200902" docName="&DRAFT;"
20  category="bcp" xml:lang="en">
21  <front>
22    <title abbrev="Bidi IRI Guidelines">Guidelines for Internationalized
23      Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
24    <author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst"
25      fullname="Martin J. Duerst (Note: Please write &quot;Duerst&quot; with u-umlaut wherever possible, for example as &quot;D&amp;#252;rst&quot; in XML and HTML.)">
26      <organization>Aoyama Gakuin University<ionly> (青山学院大学)</ionly> </organization>
27      <address>
28        <postal>
29          <street>5-10-1 Fuchinobe</street>
30          <street>Chuo-ku</street>
31          <city>Sagamihara</city>
32          <region>Kanagawa</region>
33          <code>252-5258</code>
34          <country>Japan</country>
35        </postal>
36        <phone>+81 42 759 6329</phone>
37        <facsimile>+81 42 759 6495</facsimile>
38        <email>duerst@it.aoyama.ac.jp</email>
39        <uri><aonly>http://www.sw.it.aoyama.ac.jp/D%C3%BCrst/ (Note: This is the percent-encoded form of an IRI)</aonly><ionly>http://www.sw.it.aoyama.ac.jp/Dürst/</ionly></uri>
40      </address>
41    </author>
42    <author initials="L." surname="Masinter" fullname="Larry Masinter">
43      <organization>Adobe</organization>
44      <address>
45        <postal>
46          <street>345 Park Ave</street>
47          <city>San Jose</city>
48          <region>CA</region>
49          <code>95110</code>
50          <country>U.S.A.</country>
51        </postal>
52        <phone>+1-408-536-3024</phone>
53        <email>masinter@adobe.com</email>
54        <uri>http://larry.masinter.net</uri>
55      </address>
56    </author>
57    <author initials="A." isurname="Allawi (عادل علاوي)" surname="Allawi"
58      ifullname="Adil Allawi (عادل علاوي)" fullname="Adil Allawi">
59    <organization>Diwan Software Limited</organization>
60      <address>
61        <postal>
62          <street>37-39 Peckham Road</street>
63          <city>London</city>
64          <code>SE5 8UH</code>
65          <country>United Kingdom</country>
66        </postal>
67        <phone>+44 7718 785850</phone>
68        <facsimile>+44 20 72525444</facsimile>
69        <email>adil@diwan.com</email>
70        <uri>http://ironymark.diwan.com/</uri>
71      </address>
72    </author>
73    <date year="&YEAR;" month="October" />
74    <area>Applications</area>
75    <workgroup>Internationalized Resource Identifiers (iri)</workgroup>
76    <keyword>IRI</keyword>
77    <keyword>Internationalized Resource Identifier</keyword>
78    <keyword>BIDI</keyword>
79    <keyword>URI</keyword>
80    <keyword>URL</keyword>
81    <keyword>IDN</keyword>
82    <abstract>
83      <t>This specification gives guidelines for selection, use, and
84        presentation of International Resource Identifiers (IRIs) which include
85        characters with inherent right-to-left (rtl) writing direction. </t>
86    </abstract>
87  </front>
88  <middle>
89    <section title="Introduction">
90      <section title='Overview'>
91      <t>Some UCS characters, such as those used in the Arabic and Hebrew
92        scripts, have an inherent right-to-left (rtl) writing direction as
93        opposed to characters, such as those in the Latin script, that have an
94        inherent left-to-right (ltr) direction. IRIs containing rtl characters
95        (called bidirectional IRIs or Bidi IRIs) require additional attention
96        because of the non-trivial relation between their logical and visual
97        ordering. The logical order represents the order in which characters are
98        stored on computers and read by people. The visual order is the order in
99        which the characters appear (or are expected to appear) on a computer
100        display or printout.</t>
101      <t>Generally, alphabetic characters in scripts like Arabic and Hebrew are
102        drawn rtl while numbers are drawn ltr. Symbols such as slash ('/') and
103        period ('.') take their visual direction from the surrounding characters.</t>
104      <t>Because of this complex interaction between the logical representation,
105        the visual representation, and the syntax of a Bidi IRI, a balance is
106        needed between various requirements. The main requirements are: <list
107        style="hanging">
108        <t hangText="1.">user-predictable conversion between visual and logical
109          representation;</t>
110        <t hangText="2.">the ability to include a wide range of characters in
111          various parts of the IRI; and</t>
112        <t hangText="3.">minor or no changes or restrictions for
113          implementations.</t>
114        </list></t>
115        </section>
116      <section title='Availability'>
117        <t>This document is available in (line-printer ready) plaintext ASCII and in PDF.
118          It is also available in HTML from
119          <vspace/><eref target="http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.html"
120            >http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.html</eref>,
121          and in UTF-8 plaintext from
122          <vspace/><eref target="http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.utf8.txt"
123            >http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.utf8.txt</eref>.
124          While all these versions are identical in their technical content,
125          the HTML, PDF, and UTF-8 plaintext versions show non-Unicode characters directly.
126          This often makes it easier to understand examples, and readers are therefore strongly advised
127          to consult these versions in preference or as a supplement to the ASCII version.</t>
128        <t><ionly>This version of this document contains bidirectional examples.
129          In order to correctly understand the examples, it is important to view this document
130          with a tool that correctly implements the Unicode Bidirectional Algorithm <xref target="UNI9"/>.
131           Many text viewers and text editors, and most browsers, currently implement
132           the Unicode Bidirectional Algorithm, but there are some exceptions.
133           Also, all users who are reading RTL text on a regular basis have tools
134           that implement this algorithm, because otherwise, they would be unable
135           to read even the simplest texts.
136           In order to check whether a tool implements the Unicode Bidirectional Algorithm,
137            please observe the line of Hebrew characters below:
138           <vspace/><span dir='ltr'>א, אב, אבג, אבגד, אבגדה, אבגדהו</span>
139           <vspace/>If the shortest word (one character) is on the right, and the longest word (six characters)
140           is on the left, and the words get longer and longer from right to left,
141           and the commas are between the words, but on the right of the spaces,
142           then your tool should be okay. Otherwise, please use another tool.
143           Please note that the example is only in Hebrew because in Arabic,
144           it is difficult to count characters for people who are not familiar
145           with the script.</ionly></t>
146      </section>
147      <section title="Notation">
148        <t>In this document, "Bidi Notation", abbreviated "BN" is used for the given Bidi IRI
149          examples as follows: Lower case letters a-z stand for characters that
150          are written with a left to right ordering (such as Latin characters),
151          whereas upper case letters A-Z represent characters that are written
152          right to left (such as Arabic or Hebrew characters). Numbers and
153          symbols are the same.</t>
154        <t> In this document, the key words "MUST", "MUST NOT", "REQUIRED",
155          "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
156          and "OPTIONAL" are to be interpreted as described in <xref
157            target="RFC2119"/>.</t>
158      </section>
159      <!-- Notation -->
160    </section>
161    <!-- Introduction -->
162    <section title="Logical Storage and Visual Presentation" anchor="visual">
163      <t>When stored or transmitted in digital representation, Bidi IRIs MUST be
164        in full logical order and MUST conform to the IRI syntax rules (which
165        includes the rules relevant to their scheme). This ensures that
166        Bidi IRIs can be processed in the same way as other IRIs.</t>
167      <t>Bidi IRIs MUST be visually ordered by the Unicode Bidirectional
168        Algorithm <xref target="UNIV6"/>, <xref target="UNI9"/>. Bidi IRIs MUST
169        be rendered in the same way as they would be if they were in a
170        left-to-right embedding. </t>
171      <t>In conformance with the Unicode Bidirectional Algorithm, embedding MAY
172        be done in one of two ways: <list style="hanging">
173        <t hangText="1.">precede the IRI with U+202A, LEFT-TO-RIGHT EMBEDDING
174          (LRE), and follow with U+202C, POP DIRECTIONAL FORMATTING (PDF);
175          or</t>
176        <t hangText="2.">use a higher-level protocol (e.g., the dir='ltr'
177          attribute in HTML).</t>
178        </list></t>
179      <t>Preceding and following the Bidi IRI with U+200E, LEFT-TO-RIGHT MARK
180        (LRM). Is NOT RECOMMENDED as, there are cases where this may not be
181        sufficient to match full left to right embedding.</t>
182      <t>There is no requirement to use embedding if the display is still the
183        same without the embedding. For example, a Bidi IRI in a text
184        with left-to-right base directionality (such as used for English or
185        Cyrillic) that is preceded and followed by whitespace and strong
186        left-to-right characters does not need an embedding. Also, a
187        bidirectional relative IRI reference that only contains strong
188        right-to-left characters and weak characters (such as symbols) and that
189        starts and ends with a strong right-to-left character and appears in a
190        text with right-to-left base directionality (such as used for Arabic or
191        Hebrew) and is preceded and followed by whitespace and strong characters
192        does not need an embedding.</t>
193      <t>However, Implementers are, RECOMMENDED to use embedding in all cases
194        where they are not completely sure that the display behavior is
195        unaffected without the embedding.</t>
196      <t>The Unicode Bidirectional Algorithm (<xref target="UNI9"/>, section
197        4.3) permits higher-level protocols to influence bidirectional
198        rendering. Such changes by higher-level protocols MUST NOT be used if
199        they change the rendering of IRIs.</t>
200      <t>The bidirectional formatting characters that may be used before or
201        after the IRI to ensure correct display are not themselves part of the
202        IRI. IRIs MUST NOT contain bidirectional formatting characters (LRM,
203        RLM, LRE, RLE, LRO, RLO, and PDF). They affect the visual rendering of
204        the IRI but do not appear themselves. It would therefore not be possible
205        to input an IRI with such characters correctly.</t>
206    </section>
207    <!-- visual -->
208    <section title="Bidi IRI Structure" anchor="bidi-structure">
209      <t>The Unicode Bidirectional Algorithm is designed for general purpose
210        text. To make sure that it does not affect the rendering of Bidi IRIs
211        outside of the requirements of this document, some restrictions on Bidi
212        IRIs are necessary. These restrictions are given in terms of delimiters
213        (structural characters, mostly punctuation such as "@", ".", ":", and
214        "/") and components (usually consisting mostly of letters and
215        digits).</t>
216      <t>The following syntax rules from the ABNF of <xref target="RFC3987bis"/>
217        correspond to components for the purpose of Bidi behavior: iuserinfo,
218        ireg-name, isegment, isegment-nz, isegment-nz-nc, ireg-name, iquery, and
219        ifragment.</t>
220      <t>Specifications that define the syntax of any of the above components
221        MAY divide them further and define smaller parts to be components
222        according to this document. As an example, the restrictions of <xref
223          target="RFC3490"/> on bidirectional domain names correspond to treating
224        each label of a domain name as a component for schemes with ireg-name as
225        a domain name. Even where the components are not defined formally, it
226        may be helpful to think about some syntax in terms of components and to
227        apply the relevant restrictions. For example, for the usual name/value
228        syntax in query parts, it is convenient to treat each name and each
229        value as a component. As another example, the extensions in a resource
230        name can be treated as separate components.</t>
231      <t>For each component, the following restrictions apply:</t>
232      <t> <list style="hanging">
233        <t hangText="1.">A component SHOULD NOT use both right-to-left and
234          left-to-right characters.</t>
235        <t hangText="2.">A component using right-to-left characters SHOULD start
236          with a right-to-left character, and end with a right-to-left character
237          potentially followed by one or more nonspacing mark (bidi class NSM).</t>
238      </list></t>
239      <t>The above restrictions are given as "SHOULD"s, rather than as "MUST"s.
240        For IRIs that are never presented visually, they are not relevant.
241        However, for IRIs in general, they are very important to ensure
242        consistent conversion between visual presentation and logical
243        representation, in both directions.</t>
244      <t><list style="hanging">
245        <t hangText="Note:">In some components, the above restrictions may
246          actually be strictly enforced. For example, <xref target="RFC3490"/>
247          requires that these restrictions apply to the labels of a host name
248          for those schemes where ireg-name is a host name. In some other
249          components (for example, path components) following these restrictions
250          may not be too difficult. For other components, such as parts of the
251          query part, it may be very difficult to enforce the restrictions
252          because the values of query parameters may be arbitrary character
253          sequences.</t>
254      </list></t>
255      <t>If the above restrictions cannot be satisfied otherwise, the affected
256        component can always be mapped to URI notation using the general
257        percent-encoding of IRI components, as described in <xref
258          target="RFC3987bis"/>. Please note that the whole component has to be
259        mapped (see also Example 9 below).</t>
260    </section>
261    <!-- bidi-structure -->
262    <section title="Input of Bidi IRIs" anchor="bidiInput">
263      <t>Bidi input methods MUST generate Bidi IRIs in logical order while
264        rendering them according to <xref target="visual"/>. During input,
265        rendering SHOULD be updated after every new character is input to avoid
266        end-user confusion.</t>
267    </section>
268    <!-- bidiInput -->
269    <section title="Examples">
270      <t>This section gives examples of Bidi IRIs in Bidi Notation. It shows
271        legal IRIs with the relationship between their logical and visual
272        representation and explains how certain phenomena in this relationship
273        may look strange to somebody not familiar with bidirectional behavior,
274        but familiar to users of Arabic and Hebrew. It also shows what happens
275        if the restrictions given in <xref target="bidi-structure"/> are not
276        followed. The examples below can be seen at <xref target="BidiEx"/>, in
277        Arabic, Hebrew, and Bidi Notation variants.</t>
278      <t>To read the bidi text in the examples, read the visual representation
279        from left to right until you encounter a block of rtl text. Read the rtl
280        block (including slashes and other special characters) from right to
281        left, then continue at the next unread ltr character.</t>
282      <t>Please note that "BN" stands for "Bidi Notation", see <eref target="Notation" />.
283        AR stands for Arabic, HE for Hebrew.</t>
284
285      <t>Example 1: A single component with rtl characters is inverted:
286
287        <vspace/>Logical representation (BN): "http://ab.CDEFGH.ij/kl/mn/op.html"
288        <vspace/>Visual representation (BN): "http://ab.HGFEDC.ij/kl/mn/op.html"
289        <ionly>
290        <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.تثجحخد.ij/kl/mn/op.html</span>"
291        <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.גדהוזח.ij/kl/mn/op.html</span>"
292        </ionly>
293        <vspace/>Components can be read one
294        by one, and each component can be read in its natural direction.</t>
295
296      <t>Example 2: More than one consecutive component with rtl characters is
297        inverted as a whole:
298
299        <vspace/>Logical representation (BN): "http://ab.CDE.FGH/ij/kl/mn/op.html"
300        <vspace/>Visual representation (BN): "http://ab.HGF.EDC/ij/kl/mn/op.html"
301        <ionly>
302          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.تثج.حخد/ij/kl/mn/op.html</span>"
303          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.גדה.וזח/ij/kl/mn/op.html</span>"
304        </ionly>
305       
306        <vspace/> A sequence of rtl
307        components is read rtl, in the same way as a sequence of rtl words is
308        read rtl in a bidi text.</t>
309
310      <t>Example 3: All components of an IRI (except for the scheme) are rtl.
311        All rtl components are inverted overall:
312
313        <vspace/>Logical representation (BN): "http://AB.CD.EF/GH/IJ/KL?MN=OP;QR=ST#UV"
314        <vspace/>Visual representation (BN): "http://VU#TS=RQ;PO=NM?LK/JI/HG/FE.DC.BA"
315        <ionly>
316          <vspace/>Visual representation (AR): "<span dir='ltr'>http://اب.تث.جح/خد/ذر/زس?شص=ضط;ظع=غف#قك</span>"
317          <vspace/>Visual representation (HE): "<span dir='ltr'>http://אב.גד.הו/זח/טי/כל?מן=סע;פץ=קר#שת</span>"
318        </ionly>
319       
320        <vspace/> The
321        whole IRI (except the scheme) is read rtl. Delimiters between rtl
322        components stay between the respective components; delimiters between
323        ltr and rtl components don't move.</t>
324
325      <t>Example 4: Each of several sequences of rtl components is inverted on
326        its own:
327
328        <vspace/>Logical representation (BN): "http://AB.CD.ef/gh/IJ/KL.html"
329        <vspace/>Visual representation (BN): "http://DC.BA.ef/gh/LK/JI.html"
330        <ionly>
331          <vspace/>Visual representation (AR): "<span dir='ltr'>http://اب.تث.ef/gh/ذر/زس.html</span>"
332          <vspace/>Visual representation (HE): "<span dir='ltr'>http://אב.גד.ef/gh/טי/כל.html</span>"
333        </ionly>
334       
335        <vspace/> Each sequence of rtl components
336        is read rtl, in the same way as each sequence of rtl words in an ltr
337        text is read rtl.</t>
338
339      <t>Example 5: Example 2, applied to components of different kinds:
340
341        <vspace/>Logical representation (BN): "http://ab.cd.EF/GH/ij/kl.html"
342        <vspace/>Visual representation (BN): "http://ab.cd.HG/FE/ij/kl.html"
343        <ionly>
344          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.cd.جح/خد/ij/kl.html</span>"
345          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.cd.הו/זח/ij/kl.html</span>"
346        </ionly>
347       
348        <vspace/>
349        The inversion of the domain name label and the path component may be
350        unexpected, but it is consistent with other bidi behavior. For
351        reassurance that the domain component really is "ab.cd.EF", it may be
352        helpful to read aloud the visual representation following the Unicode
353        Bidirectional Algorithm. After "http://ab.cd." one reads the RTL block
354        "E-F-slash-G-H", which corresponds to the logical representation. </t>
355
356      <t>Example 6: Same as Example 5, with more rtl components:
357       
358        <vspace/>Logical representation (BN): "http://ab.CD.EF/GH/IJ/kl.html"
359        <vspace/>Visual representation (BN): "http://ab.JI/HG/FE.DC/kl.html"
360        <ionly>
361          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.تث.جح/خد/ذر/kl.html</span>"
362          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.גד.הו/זח/טי/kl.html</span>"
363        </ionly>
364       
365        <vspace/> The inversion of the domain
366        name labels and the path components may be easier to identify because
367        the delimiters also move.</t>
368     
369      <t>Example 7: A single rtl component includes digits:
370
371        <vspace/>Logical representation (BN): "http://ab.CDE123FGH.ij/kl/mn/op.html"
372        <vspace/>Visual representation (BN): "http://ab.HGF123EDC.ij/kl/mn/op.html"
373        <ionly>
374          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.تثج123حخد.ij/kl/mn/op.html</span>"
375          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.גדה123וזח.ij/kl/mn/op.html</span>"
376        </ionly>
377       
378        <vspace/> Numbers
379        are written ltr in all cases but are treated as an additional embedding
380        inside a run of rtl characters. This is completely consistent with usual
381        bidirectional text.</t>
382
383      <t>Example 8 (not allowed): Numbers are at the start or end of an rtl
384        component:
385       
386        <vspace/>Logical representation (BN): "http://ab.cd.ef/GH1/2IJ/KL.html"
387        <vspace/>Visual representation (BN): "http://ab.cd.ef/LK/JI1/2HG.html"
388        <ionly>
389          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.cd.ef/خد1/2ذر/زس.html</span>"
390          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.cd.ef/זח1/2טי/כל.html</span>"
391        </ionly>
392       
393        <vspace/> The sequence "1/2" is
394        interpreted by the Bidirectional Algorithm as a fraction, fragmenting the
395        components and leading to confusion. There are other characters that are
396        interpreted in a special way close to numbers; in particular, "+", "-",
397        "#", "$", "%", ",", ".", and ":".</t>
398
399      <t>Example 9 (not allowed): The numbers in the previous example are
400        percent-encoded:
401       
402        <vspace/>Logical representation (BN): "http://ab.cd.ef/GH%31/%32IJ/KL.html"
403        <vspace/>Visual representation (BN): "http://ab.cd.ef/LK/JI%32/%31HG.html"
404        <ionly>
405          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.cd.ef/خد%31/%32ذر/زس.html</span>"
406          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.cd.ef/זח%31/%32טי/כל.html</span>"
407        </ionly>
408       
409      </t>
410     
411      <t>Example 10 (allowed but not recommended):
412       
413        <vspace/>Logical representation (BN): "http://ab.CDEFGH.123/kl/mn/op.html"
414        <vspace/>Visual representation (BN): "http://ab.123.HGFEDC/kl/mn/op.html"
415        <ionly>
416          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.تثجحخد.123/kl/mn/op.html</span>"
417          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.גדהוזח.123/kl/mn/op.html</span>"
418        </ionly>
419       
420        <vspace/> Components
421        consisting of only numbers are allowed (it would be rather difficult to
422        prohibit them), but these may interact with adjacent RTL components in
423        ways that are not easy to predict.</t>
424
425      <t>Example 11 (allowed but not recommended):
426       
427        <vspace/>Logical representation (BN): "http://ab.CDEFGH.123ij/kl/mn/op.html"
428        <vspace/>Visual representation (BN): "http://ab.123.HGFEDCij/kl/mn/op.html"
429        <ionly>
430          <vspace/>Visual representation (AR): "<span dir='ltr'>http://ab.تثجحخد.123ij/kl/mn/op.html</span>"
431          <vspace/>Visual representation (HE): "<span dir='ltr'>http://ab.גדהוזח.123ij/kl/mn/op.html</span>"
432        </ionly>
433       
434        <vspace/>
435        Components consisting of numbers and left-to-right characters are
436        allowed, but these may interact with adjacent RTL components in ways
437        that are not easy to predict.</t>
438    </section>
439    <!-- examples -->
440    <section title="IANA Considerations" anchor="iana">
441      <t>This document makes no changes to IANA registries.</t>
442    </section>
443    <!-- IANA -->
444    <section title="Security Considerations" anchor="security">
445      <t>Confusion can occur with bidirectional IRIs, if the restrictions in
446        <xref target="bidi-structure"/> are not followed. The same visual
447        representation may be interpreted as different logical representations,
448        and vice versa. It is also very important that a correct Unicode
449        bidirectional implementation be used.</t>
450    </section>
451    <!-- security -->
452    <section title="Acknowledgements">
453      <t>This document was derived from <xref target="RFC3987"/> and <xref
454        target="RFC3987bis"/> and the acknowledgments of those documents
455        apply. Shunsuke Oshima (大嶋 俊介) provided the data for Appendix A.</t>
456    </section>
457    <!-- acknowledgements -->
458    <section title="Main Changes Since RFC 3987">
459      <t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>       
460        <t>Note to RFC Editor: Please remove this paragraph before publication.
461          Detailled change logs are available in the IETF tools subversion repository at
462          http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/draft-ietf-iri-bidi-guidelines.xml.</t>
463       
464      <t><list style="symbols">
465        <t>Separated out the section on bidi in <xref target="RFC3987"/> to this document.</t>
466        <t>Added examples in Arabic and Hebrew, which can be seen in html/pdf/utf8.txt versions.</t>
467        <t>Allowed NSMs at the end of components, for Dhivehi, Yiddish,...</t>
468        <t>TODO: check for major changes between RFC3987 and draft -02.</t>
469      </list>
470      </t>
471    </section>
472  </middle>
473  <back>
474    <references title="Normative References">
475      <reference anchor="RFC3987bis"
476        target="http://tools.ietf.org/id/draft-ietf-iri-3987bis">
477        <front>
478          <title>Internationalized Resource Identifiers (IRIs)</title>
479          <author initials="M." surname="Duerst"/>
480          <author initials="L." surname="Masinter" fullname="Larry Masinter"/>
481          <author initials="M." surname="Suignard"/>
482          <date year="2011" month="August" day="14"/>
483        </front>
484      </reference>
485      &rfc2119;
486      &rfc3490;
487      <reference anchor="UNIV6">
488        <front>
489          <title>The Unicode Standard, Version 6.0.0 (Mountain View, CA, The
490            Unicode Consortium, 2011, ISBN 978-1-936213-01-6)</title>
491          <author>
492            <organization>The Unicode Consortium</organization>
493          </author>
494          <date year="2010" month="October"/>
495        </front>
496      </reference>
497      <reference anchor="UNI9"
498        target="http://www.unicode.org/reports/tr9/tr9-13.html">
499        <front>
500          <title>The Unicode Bidirectional Algorithm</title>
501          <author initials="M." surname="Davis" fullname="Mark Davis">
502            <organization/>
503          </author>
504          <date year="2004" month="March"/>
505        </front>
506        <seriesInfo name="Unicode Standard Annex" value="#9"/>
507      </reference>
508    </references>
509    <references title="Informative References">
510      <reference anchor="BidiEx"
511        target="http://www.w3.org/International/iri-edit/BidiExamples">
512        <front>
513          <title>Examples of Bidi IRIs</title>
514          <author>
515            <organization/>
516          </author>
517          <date year="" month=""/>
518        </front>
519      </reference> &rfc3987; </references>
520    <section title='List of ASCII Symbols and their Bidirectional Character Types'>
521      <t>To help understand the influence of various symbols on IRI display,
522        this appendix lists all of them, giving the character itself,
523        the Unicode codepoint, the character name, the bidirectional character type (BCT)
524        and the rule and relevance in the IRI syntax.</t>
525      <t>The most important ones in practice are
526        ":", delimining schem and port (CS, Common Number Separator),
527        "/" to indicate generic (hierarchical) schemes and as a path separator (CS, Common Number Separator),
528        "?" to introduce a query part (ON, Other Neutral),
529        "#" to introduce a fragment identifier (ET, European Number Terminator),
530        "." to separate labels in a domain name (CS, Common Number Separator),
531        "&amp;" to separate form parameters (ON, Other Neutral), and
532        "@" to separate user information (ON, Other Neutral).
533      </t>
534      <figure>
535        <artwork>
536Char Codepoint  Character Name       BCT  IRI syntax
537-------------------------------------------------------------
538"#"  U+0023     NUMBER SIGN          ET   gen-delims, fragments
539"/"  U+002F     SOLIDUS              CS   gen-delims, paths
540":"  U+003A     COLON                CS   gen-delims, scheme, port
541"?"  U+003F     QUESTION MARK        ON   gen-delims, query part
542"@"  U+0040     COMMERCIAL AT        ON   gen-delims, user
543"["  U+005B     LEFT SQUARE BRACKET  ON   gen-delims
544"]"  U+005D     RIGHT SQUARE BRACKET ON   gen-delims
545"%"  U+0025     PERCENT SIGN         ET   pcd-encoded
546"!"  U+0021     EXCLAMATION MARK     ON   sub-delims
547","  U+002C     COMMA                CS   sub-delims
548"+"  U+002B     PLUS SIGN            ES   sub-delims
549"$"  U+0024     DOLLAR SIGN          ET   sub-delims
550"("  U+0028     LEFT PARENTHESIS     ON   sub-delims
551"'"  U+0027     APOSTROPHE           ON   sub-delims
552")"  U+0029     RIGHT PARENTHESIS    ON   sub-delims
553"*"  U+002A     ASTERISK             ON   sub-delims
554";"  U+003B     SEMICOLON            ON   sub-delims
555"="  U+003D     EQUALS SIGN          ON   sub-delims, forms
556"&amp;"  U+0026     AMPERSAND            ON   sub-delims, forms
557"."  U+002E     FULL STOP            CS   unreserved, domain names
558"-"  U+002D     HYPHEN-MINUS         ES   unreserved
559"_"  U+005F     LOW LINE             ON   unreserved
560"~"  U+007E     TILDE                ON   unreserved
561" "  U+0020     SPACE                WS   excluded, delim
562'"'  U+0022     QUOTATION MARK       ON   excluded, delim
563"\"  U+005C     REVERSE SOLIDUS      ON   excluded, unwise
564"^"  U+005E     CIRCUMFLEX ACCENT    ON   excluded, unwise
565"&lt;"  U+003C     LESS-THAN SIGN       ON   excluded, delim
566">"  U+003E     GREATER-THAN SIGN    ON   excluded, delim
567"`"  U+0060     GRAVE ACCENT         ON   excluded, unwise
568"|"  U+007C     VERTICAL LINE        ON   excluded, unwise
569"{"  U+007B     LEFT CURLY BRACKET   ON   excluded, delim
570"}"  U+007D     RIGHT CURLY BRACKET  ON   excluded, delim
571        </artwork>
572      </figure>
573    </section>
574  </back>
575</rfc>
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