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xfq merged 4 commits into from
Jun 16, 2026
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Add explanation for "halfwidth" term usage in typography #742

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Add explanation for "halfwidth" term usage in typography
xfq Mar 11, 2026
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typo fix
xfq Apr 15, 2026
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editorial fix
xfq Apr 15, 2026
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edits per telecon
xfq Apr 15, 2026
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Expand Up @@ -1008,6 +1008,11 @@ <h3>
<p its-locale-filter-list="en" lang="en">Formerly, <a href="#term.fullwidth" class="termref">fullwidth</a> ASCII characters were often used, either to make the presentation look orderly, or simply due to the poorly developed computer technologies available for text layout. Nowadays, typesetting engines allow for proportional or monospace fonts, as required, rather than forcing the user to resort to the old fullwidth blocks of Latin letters and European numerals.</p>
<p its-locale-filter-list="zh-hans" lang="zh-hans">过去，由于计算机排版技术不精良，多使用“<a href="#term.fullwidth" class="termref">全角</a>ASCII字符”以达到整齐等视觉排版效果。现今在文本储存时，应避免使用该区段的拉丁字母及数字字符，交由排版引擎处理比例字体、等宽字体等显示需求。</p>
<p its-locale-filter-list="zh-hant" lang="zh-hant">過去，因計算機排版技術不甚精良，多使用「<a href="#term.fullwidth" class="termref">全形</a>ASCII字元」以達整齊等視覺排版效果。現今在文本儲存時，應避免使用該區段之拉丁字母及數字字元，交由排版引擎處理比例字體、等寬字體等顯示需求。</p>
<div class="note" id="n061">
<p its-locale-filter-list="en" lang="en" class="checkme">In everyday Chinese usage, the term "<a href="#term.halfwidth" class="termref">halfwidth</a>" is often used to refer to ASCII characters, including Latin letters, European numerals, and some Western symbols. In typography, however, "halfwidth" and "<a href="#term.fullwidth" class="termref">fullwidth</a>" serve as concepts for measuring character width. Strictly speaking, a character can only be designated as "halfwidth" if its width is precisely half that of a fullwidth character. Since the vast majority of Western fonts used in modern publications are proportional fonts and the widths of individual characters vary, it is inaccurate to collectively label all such characters as "halfwidth".</p>

@aphillips aphillips Apr 15, 2026 •
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There are a lot of interesting quirks buried in here.

Historically, half-width characters were encoded as a single byte and full-width characters as two bytes in legacy encodings (such as GB2312, Big5, ISO-2022-x, etc.). The bytes corresponded to screen positions on terminals or line printers (where the fonts can never be proportional).

These relationships were encoded into the East Asian Width properties in Unicode, since the Unicode character encodings don't preserve the byte-width. Character "width" still mattered for screen layout. In Asian typography and fonts, half-width characters generally have glyphs that are half the width--the better to preserve the layout grid--while Western/non-Asian fonts use proportional glyphs (making grid management much more difficult). Mixing fonts, as is done in modern systems, makes the half-width/full-width distinction artificial and frequently misleading.

To that extent, I agree with your definition here, except to note that it is somewhat font-dependent. The half/full distinction often would apply if a Chinese font were used for the characters and it does remain a property of certain characters to be "half" or "full" width with regard to Unicode. You might want to include more of the above history/explanation (suitably corrected where needed)?

(Not important to Chinese, but Japanese has half-width katakana characters that are drawn narrowly for UX which have roots in 8859 national character standards, where the narrow katakana were 1-byte and full-width characters in Shift-JIS were two bytes)

@xfq xfq May 20, 2026

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Thank you for your thoughts, Addison! In today's TF telecon, we decided to keep this note simple and not include too much historical content, intending to merge it as it is now.

<p its-locale-filter-list="zh-hans" lang="zh-hans">在日常用语中，“<a href="#term.halfwidth" class="termref">半角</a>”常被宽泛地用来指代ASCII字符，通常包括拉丁字母、阿拉伯数字及部分西文符号等。在排版上，“半角”与“<a href="#term.fullwidth" class="termref">全角</a>”是度量宽度的概念，只有在这些字符的宽度为全角字符的一半时，称其为“半角”才严格成立。现代出版物中使用的西文字体，绝大多数是比例字体，各字符宽度并不一致，因此将这些字符一概称为“半角”并不准确。</p>
<p its-locale-filter-list="zh-hant" lang="zh-hant">在日常用語中，「<a href="#term.halfwidth" class="termref">半形</a>」常被寬泛地用來指代ASCII字元，通常包括拉丁字母、阿拉伯數字及部分西文符號等。在排版上，「半形」與「<a href="#term.fullwidth" class="termref">全形</a>」是度量寬度的概念。只有在這些字元的字幅為全角字元的一半時，稱其為「半形」才嚴格成立。現代出版物中使用的西文字體，絕大多數是比例字體，各字元寬度並不一致，因此將這些字元一概稱為「半形」並不準確。</p>
</div>
<p its-locale-filter-list="en" lang="en">When Western texts are mixed with Han characters, Chinese style punctuation and its common usage should be used in principle since the main text is Chinese. However, in the case of technical documents, if plenty of formulae are contained in the text, the full stop can be unified with the western-style period, <span class="uname" translate="no">U+002E FULL STOP</span> [.], and the ellipsis can be unifed with the western-style ellipsis, <span class="uname" translate="no">U+2026 HORIZONTAL ELLIPSIS</span> […]. The way glyphs are positioned relative to the character frame follows the Western convention for both Simplified and Traditional text. Also in textbooks on the grammar of Western languages, which contain plenty of example sentences mixed with Chinese, the aforementioned western-style periods can be used.</p>
<p its-locale-filter-list="zh-hans" lang="zh-hans">中西混排中，由于正文是中文，原则上应该使用中文标点，遵守中文标点的习惯用法。但是，涉及公式较多的科学技术中文图书，句号可以统一使用西文句号<span class="uname" translate="no">U+002E FULL STOP</span> [.]，省略号可以使用西文省略号U+2026 HORIZONTAL ELLIPSIS […]，字面分布按西文习惯；又或西文例句较多且多与中文混排的中文版西文语法教材，亦可使用前述的西文句号。</p>
<p its-locale-filter-list="zh-hant" lang="zh-hant">中西混排中，由於正文是中文，原則上應該使用中文標點，遵守中文標點的習慣用法。但是，涉及公式較多的科學技術中文圖書，句號可以統一使用西文句號<span class="uname" translate="no">U+002E FULL STOP</span> [.]，刪節號可以使用西文刪節號U+2026 HORIZONTAL ELLIPSIS […]，字面分布按西文習慣；又或西文例句較多且多與中文混排的中文版西文語法教材，亦可使用前述的西文句號。</p>
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