为什么不'；t更多/所有Unicode'；s的左右箭头是否匹配（尤其是“黑色”箭头）？

Unicode有一系列箭头，但其中许多箭头没有匹配的左右版本。特别是，“黑色”箭头（对我来说）在导航相关任务中使用得最明显，它没有一个通常“匹配”的左右版本：➡ 通常看起来不像⬅.

很明显，对于字体，这里有一个自由裁量权：对于某些字体，它们确实匹配。但即使是FileFormat.info上的页面也显示了不同的字符：与

知道是什么吗？（对我来说）很明显，对于Unicode中包含的任何箭头，您都希望匹配（事实上，在所有四个基本方向上）。对于这种特定类型的箭头，和箭头匹配。甚至还有与“角”匹配的箭头

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注意：我就这个相关问题发表了相关评论：

右箭头和所有其他丁巴狗都是在Unicode 1.1.0中引入的。它有足够的时间“定制”成一个“丁巴”，足以与4.0.0中引入的左箭头不匹配。他们应该匹配吗？当然但并非所有符号字体都同时包含丁巴符号和其他符号和箭头。

请注意，Unicode名称列表文件包含以下注释：

 ➡  27A1        BLACK RIGHTWARDS ARROW
        * fonts may harmonize this glyph with the style for other black arrows
        x (leftwards black arrow - 2B05)
 ⬅  2B05        LEFTWARDS BLACK ARROW
        x (black rightwards arrow - 27A1)

因此，字体是受欢迎的，但不是必需的，使其看起来像其他黑色箭头。以下是如何检查所有黑色箭头：

还请注意，这些代码点未标记为bidi镜像。它们不会出现在BidMirroring文件中，该文件只有以下内容：

$ grep ARROW BidiMirroring.txt
# 29A8; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING UP AND RIGHT
# 29A9; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING UP AND LEFT
# 29AA; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING DOWN AND RIGHT
# 29AB; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING DOWN AND LEFT
# 29AC; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING RIGHT AND UP
# 29AD; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING LEFT AND UP
# 29AE; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING RIGHT AND DOWN
# 29AF; MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING LEFT AND DOWN
# 2A17; INTEGRAL WITH LEFTWARDS ARROW WITH HOOK

如果您检查这两个代码点的属性，您将看到它们的细微差别：

$ uniprops -a 27A1 2B05
U+27A1 ‹➡› \N{BLACK RIGHTWARDS ARROW}
    \pS \p{So}
    All Any Assigned InDingbats Common Zyyy Dingbats So S Gr_Base Grapheme_Base Graph GrBase Other_Symbol Pat_Syn Pattern_Syntax PatSyn Print Symbol
       X_POSIX_Graph X_POSIX_Print
    Age=1.1 Bidi_Class=ON Bidi_Class=Other_Neutral BC=ON Block=Dingbats Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered CCC=NR
       Canonical_Combining_Class=NR Script=Common Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
       Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group JG=NoJoiningGroup
       Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=AL Line_Break=Alphabetic LB=AL Numeric_Type=None NT=None Numeric_Value=NaN NV=NaN
       Present_In=1.1 IN=1.1 Present_In=2.0 IN=2.0 Present_In=2.1 IN=2.1 Present_In=3.0 IN=3.0 Present_In=3.1 IN=3.1 Present_In=3.2 IN=3.2 Present_In=4.0
       IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1 Present_In=5.2 IN=5.2 Present_In=6.0 IN=6.0 SC=Zyyy Script=Zyyy
       Sentence_Break=Other SB=XX Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX
U+2B05 ‹⬅› \N{LEFTWARDS BLACK ARROW}
    \pS \p{So}
    All Any Assigned InMiscellaneousSymbolsAndArrows Common Zyyy So S Gr_Base Grapheme_Base Graph GrBase Miscellaneous_Symbols_And_Arrows Other_Symbol
       Pat_Syn Pattern_Syntax PatSyn Print Symbol X_POSIX_Graph X_POSIX_Print
    Age=4.0 Bidi_Class=ON Bidi_Class=Other_Neutral BC=ON Block=Miscellaneous_Symbols_And_Arrows Canonical_Combining_Class=0
       Canonical_Combining_Class=Not_Reordered CCC=NR Canonical_Combining_Class=NR Script=Common Decomposition_Type=None DT=None East_Asian_Width=Neutral
       Grapheme_Cluster_Break=Other GCB=XX Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA
       Joining_Group=No_Joining_Group JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=AL Line_Break=Alphabetic LB=AL
       Numeric_Type=None NT=None Numeric_Value=NaN NV=NaN Present_In=4.0 IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1
       Present_In=5.2 IN=5.2 Present_In=6.0 IN=6.0 SC=Zyyy Script=Zyyy Sentence_Break=Other SB=XX Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX

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我有同样的问题，为什么这两支箭不匹配。看起来很傻。总之，在中有更好的匹配箭头选择，整个列表都在这里

因此，如果它们应该匹配，为什么“应该的力量”没有引入匹配的右箭头？名称（黑色向右箭头与黑色向左箭头）甚至不一致。好像他们计划引入一个匹配的向右箭头然后。。。没有，但这不是唯一的洞。数学字母数字符号、上标和下标缺少一组字符。在我的系统charmap中，我在unicode组“arrows”下有一整套匹配箭头，从\u2190到\u21ff@guido当前位置但是没有一个是黑色箭头。是的，没错，但是阅读这个问题没有提到黑色箭头（除了对发布问题的用户来说，它们是最“明显”的箭头，这一点也值得怀疑）；人们可能会认为，在unicode中，没有匹配的箭头显示此页面……然后我发现Windows 7中的默认字体甚至不包括黑色箭头。每次我倾向于给Microsoft更多的信任时，都会发生类似的事情。这也很有趣-我还以为是2012年。这取决于字体。例如三角形（

◄►或◄►) 有些字体看起来很不一样，但像Arial这样的字体显示的大小是一样的。有趣。我想最初的想法是，字形的用户只会在软件中镜像它们？（似乎违反了针对常见情况进行优化的原则。）但我仍然不明白为什么，如果添加了左、上、下箭头，a（强制）“和谐”的权利也没有被加上。这看起来就像是一个明显的疏忽。
$ uniprops -a 27A1 2B05
U+27A1 ‹➡› \N{BLACK RIGHTWARDS ARROW}
    \pS \p{So}
    All Any Assigned InDingbats Common Zyyy Dingbats So S Gr_Base Grapheme_Base Graph GrBase Other_Symbol Pat_Syn Pattern_Syntax PatSyn Print Symbol
       X_POSIX_Graph X_POSIX_Print
    Age=1.1 Bidi_Class=ON Bidi_Class=Other_Neutral BC=ON Block=Dingbats Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered CCC=NR
       Canonical_Combining_Class=NR Script=Common Decomposition_Type=None DT=None East_Asian_Width=Neutral Grapheme_Cluster_Break=Other GCB=XX
       Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA Joining_Group=No_Joining_Group JG=NoJoiningGroup
       Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=AL Line_Break=Alphabetic LB=AL Numeric_Type=None NT=None Numeric_Value=NaN NV=NaN
       Present_In=1.1 IN=1.1 Present_In=2.0 IN=2.0 Present_In=2.1 IN=2.1 Present_In=3.0 IN=3.0 Present_In=3.1 IN=3.1 Present_In=3.2 IN=3.2 Present_In=4.0
       IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1 Present_In=5.2 IN=5.2 Present_In=6.0 IN=6.0 SC=Zyyy Script=Zyyy
       Sentence_Break=Other SB=XX Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX
U+2B05 ‹⬅› \N{LEFTWARDS BLACK ARROW}
    \pS \p{So}
    All Any Assigned InMiscellaneousSymbolsAndArrows Common Zyyy So S Gr_Base Grapheme_Base Graph GrBase Miscellaneous_Symbols_And_Arrows Other_Symbol
       Pat_Syn Pattern_Syntax PatSyn Print Symbol X_POSIX_Graph X_POSIX_Print
    Age=4.0 Bidi_Class=ON Bidi_Class=Other_Neutral BC=ON Block=Miscellaneous_Symbols_And_Arrows Canonical_Combining_Class=0
       Canonical_Combining_Class=Not_Reordered CCC=NR Canonical_Combining_Class=NR Script=Common Decomposition_Type=None DT=None East_Asian_Width=Neutral
       Grapheme_Cluster_Break=Other GCB=XX Grapheme_Cluster_Break=XX Hangul_Syllable_Type=NA Hangul_Syllable_Type=Not_Applicable HST=NA
       Joining_Group=No_Joining_Group JG=NoJoiningGroup Joining_Type=Non_Joining JT=U Joining_Type=U Line_Break=AL Line_Break=Alphabetic LB=AL
       Numeric_Type=None NT=None Numeric_Value=NaN NV=NaN Present_In=4.0 IN=4.0 Present_In=4.1 IN=4.1 Present_In=5.0 IN=5.0 Present_In=5.1 IN=5.1
       Present_In=5.2 IN=5.2 Present_In=6.0 IN=6.0 SC=Zyyy Script=Zyyy Sentence_Break=Other SB=XX Sentence_Break=XX Word_Break=Other WB=XX Word_Break=XX