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Variant form (Unicode)
Variant form (Unicode)
Variant form (Unicode)
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A variant form is an alternate glyph for a character, encoded in Unicode through the mechanism of variation sequences: sequences in Unicode that consist of a base character followed by a variation selector character.

A variant form usually has a very similar appearance and meaning as its base form. The mechanism is intended for variant forms where, generally, if the variant form is unavailable, displaying the base character does not change the meaning of the text, and may not even be noticeable to many readers.

Unicode defines two types of variation sequences:

  • Standardized variation sequences defined in StandardizedVariants.txt[1]
  • Ideographic variation sequences defined in the Ideographic Variation Database (IVD)[2][3]

Variation selector characters reside in several Unicode blocks:

Variation selectors are not required for Arabic and Latin cursive characters, where substitution of glyphs can occur based on context: glyphs may be connected together depending on whether the character is the initial character in a word, the final character, a medial character or an isolated character. These types of glyph substitution are easily handled by the context of the character with no other authoring input involved. Authors may also use special-purpose characters such as joiners and non-joiners to force an alternate form of glyph where it would not otherwise appear. Ligatures are similar instances where glyphs may be substituted simply by turning ligatures on or off as a rich text attribute.

For other glyph substitution, the author's intent may need to be encoded with the text and cannot be determined contextually. This is the case with character/glyphs referred to as gaiji, where different glyphs are used for the same character either historically or for ideographs for family names. This is one of the gray areas in distinguishing between a glyph and a character: If a family name differs slightly from the ideograph character it derives from, then is that a simple glyph variant or a character variant?

Character substitutions may also occur outside of Unicode, for example with OpenType Layout tags.[4]

Blocks with standardized variation sequences

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As of Unicode version 17.0, standardized variation sequences specifically for emoji/text presentation are defined for base characters in 20 blocks:[1]

Other standardized variation sequences are formed with base characters in the following sixteen blocks:[1]

Blocks with ideographic variation sequences

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As of 14 July 2025, ideographic variation sequences are defined for base characters in eleven blocks:[2][3]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Variant form (Unicode)

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In Unicode, a variant form refers to an alternative visual representation or glyphic style for a specific character code point, allowing text processors to select distinct appearances without encoding entirely new characters. This mechanism supports diverse linguistic, cultural, and stylistic needs, such as differing typographic conventions in scripts like CJK ideographs or presentations. The primary method for specifying variant forms involves Variation Selectors, 256 non-printing characters across two blocks—the first (U+FE00–U+FE0F, 16 selectors) and the second (U+E0100–U+E01EF, 240 selectors)—that immediately follow a base character to indicate a preferred variant. These selectors do not alter the character's semantics but influence rendering by restricting choices in fonts that support them, ensuring compatibility across systems. For instance, Variation Selector-1 (U+FE00) might select a bold or italic variant for mathematical symbols, while Variation Selector-16 (U+FE0F) defaults to presentation for certain characters. Unicode defines three main categories of variant sequences using these selectors: standardized variants, ideographic variants, and emoji variants. Standardized variants, documented in the StandardizedVariants.txt file, cover over 1,000 sequences for elements like , arrows, and mathematical operators, guaranteeing consistent cross-platform rendering—such as a non-fullwidth left single (U+2018 U+FE00). Ideographic variants, managed through the Unicode Ideographic Variation Database (UTS #37), address glyph differences in Han characters for regions like or Korea, with registered sequences in IVD_Sequences.txt to preserve distinctions lost in unification. Emoji variants, outlined in UTS #51 and emoji-variation-sequences.txt, allow toggling between text-style (e.g., U+0023 U+FE0E for black-and-white "#") and emoji-style (U+0023 U+FE0F for colorful "#") presentations, supporting over 100 such pairs. Beyond selectors, accommodates variant forms through compatibility character blocks, such as Small Form Variants (U+FE50–U+FE6B), which provide superscript-like or subscript-sized (e.g., small U+FE50) for legacy compatibility, and CJK Compatibility Forms (U+FE30–U+FE4F) for vertical adjustments. These approaches ensure variant forms remain stable under normalization processes like NFC or NFD (UAX #15), where sequences are preserved to avoid unintended glyph changes during text collation or searching. Overall, variant forms enhance 's flexibility for global text interchange, balancing unification of similar with the need for precise, locale-specific rendering in applications ranging from digital to international software localization.

Fundamentals

Definition and Purpose

In , a variant form refers to an alternate representation for a single , realized through a variation sequence consisting of a base character followed by a variation selector. Variation selectors are non-spacing, default-ignorable characters that specify a restriction on the glyphs used to render the preceding base character, or select among variants sharing the same semantics but differing substantially in appearance. These sequences ensure that the base character's meaning remains unchanged while allowing tailored visual forms. The core purpose of variant forms is to accommodate diverse typographic needs—such as stylistic preferences, compatibility requirements, or regional conventions (for instance, simplified versus traditional in CJK ideographs)—without proliferating the Unicode character repertoire. By reusing code points via variation selectors, the standard avoids encoding separate characters for each variant, thereby preventing an unsustainable expansion of the codespace while upholding semantic consistency in text processing and interchange. This mechanism is particularly vital in plain-text contexts where control over fonts or rendering styles is limited, enabling reliable cross-platform rendering. Variant forms were first introduced in 3.2 in 2002 to handle glyph variability in complex scripts like Han and Mongolian, with the initial set of 16 variation selectors defined for standardized sequences. The feature has continued to evolve, incorporating additional selectors and sequences up to Unicode 17.0, released on September 9, 2025. Among its key benefits, variant forms enhance interoperability by standardizing glyph choices across diverse fonts and systems, support cultural and linguistic representation through precise variant selection, and improve accessibility by preserving distinctions that might otherwise be lost in normalization processes. Variation selectors serve as the dedicated Unicode characters (such as those in the range U+FE00–U+FE0F) that form these sequences.

Variation Selectors

Variation selectors are nonspacing combining characters that immediately follow a base character to specify a particular variant for that base, without altering its semantics or core identity. They function by restricting or selecting from the possible representations of the preceding character, enabling precise control over visual appearance in contexts such as different scripts or stylistic preferences. Unicode defines variation selectors in two primary blocks: the Variation Selectors block from U+FE00 to U+FE0F, which contains 16 selectors (VS1 through VS16) intended for general use, and the Variation Selectors Supplement block from U+E0100 to U+E01EF, which provides 240 additional selectors (VS17 through VS256) primarily reserved for ideographic applications. The first 16 selectors support both standardized variation sequences—defined for specific base characters across various scripts—and ideographic variation sequences, while VS17 to VS256 are exclusively for ideographic use, as registered in the Ideographic Variation Database. The original set of 16 variation selectors was introduced in 3.2 in 2002 to address the need for variant selection in emerging digital text processing. The Variation Selectors Supplement block was added in 4.0 in 2005, expanding capacity specifically for complex ideographic systems, with the overall framework remaining stable through expansions in registered sequences up to 17.0. These selectors exhibit non-visual behavior, classified as combining marks with a combining class of 0, making them default ignorable and invisible in rendering unless they form a recognized variation sequence; they do not influence text directionality, line breaking, or bidirectional ordering.

Types of Variation Sequences

Standardized Variation Sequences

Standardized variation sequences consist of a single base character followed by one of the variation selectors (U+FE00 through U+FE0F) to specify a particular for the base character, with these sequences explicitly defined in the Standard and its associated data files. Unlike ideographic variation sequences, which are registered in an external database for extensibility, standardized sequences are fixed and do not require additional registration processes. These sequences are used to control specific visual appearances across various scripts and symbol categories. For emoji presentation control, sequences like U+26BD U+FE0E (soccer ball in text style, rendering as a monochrome outline) and U+26BD U+FE0F (soccer ball in style, rendering as a colorful pictograph) allow selection between textual and graphical forms. In mathematical contexts, examples include U+0030 U+FE00 (digit zero with a short diagonal variant), providing precise glyph forms for technical notation in blocks such as Mathematical Operators. Compatibility ideographs, such as U+349E U+FE00 (mapping to CJK Compatibility Ideograph-2F80C), ensure consistent rendering of legacy forms in the CJK Compatibility Ideographs block. The sequences are primarily associated with blocks including (for emoji variants), , Mathematical Operators, and CJK Compatibility Ideographs. As of Unicode 17.0, over 900 such sequences are defined across the relevant data files, with 614 in the core StandardizedVariants.txt and 371 emoji-specific ones. Usage is constrained to the specific base characters listed in the documentation; any unrecognized sequence defaults to rendering the base character alone without alteration, ensuring and preventing unintended changes.

Ideographic Variation Sequences

Ideographic variation sequences (IVS) consist of a base ideographic character followed by one of the variation selectors from VS17 (U+E0100) to VS256 (U+E01EF), which specify particular variants for the base character, such as historical, regional, or stylistic forms in scripts like CJK. These sequences enable the selection of specific renderings without altering the underlying character identity, supporting extensibility for ideographs beyond the fixed standardized variation sequences defined in the Standard. The Unicode Ideographic Variation Database (IVD) serves as the official registry for these sequences, maintained by the to ensure consistent and interoperable use across systems. It organizes IVS into collections sourced from authoritative bodies, including the Ideographic Research Group (IRG) for Han ideographs and the Moji_Joho project in for Japanese variants, among others. This structure allows for the documentation of glyphic subsets associated with each registered sequence, facilitating reliable text interchange in applications requiring precise ideograph rendering. Registration of new IVS occurs through a formal process governed by Technical Standard #37, where submitters propose sequences along with representative glyph samples for review. Proposals undergo a public review period of at least 90 days, potentially extended for larger submissions exceeding 4,000 sequences, after which approved sequences are added to the IVD by the designated registrar. The most recent update to the IVD, dated July 14, 2025, incorporated the new CAAPH collection for Chinese ancient texts, along with charts for existing collections such as MSARG ( Advanced Research Group) and KRName (Korean names), expanding support for specialized variants. As of July 2025, the IVD contains 39,501 registered sequences applicable to base characters across 11 blocks, including , providing extensive coverage for variant forms in East Asian scripts. Major collections, such as Adobe-Japan1 with 14,684 sequences and Hanyo-Denshi with 13,045, demonstrate the database's growth and utility for professional and digital archiving. Only sequences explicitly registered in the IVD are considered standardized for conformant implementations; unregistered combinations of base ideographs and variation selectors are ignored to maintain stability and prevent unintended substitutions. This validation mechanism ensures that IVS enhance rather than complicate the encoding model.

Applications

CJK Ideographs

In the Unicode Standard, Han unification combines ideographs from the Chinese, Japanese, and Korean (CJK) writing systems into shared code points to reduce redundancy while maintaining semantic identity across languages. This process, however, necessitates variant forms to accommodate regional and historical glyph differences, such as simplified characters used in versus traditional forms in and , (postwar simplified) versus (prewar) forms in Japanese, and analogous distinctions in Korean . Ideographic Variation Sequences (IVS) provide a mechanism to specify these variants by appending a variation selector to a base ideograph, enabling precise control over selection in digital text without expanding the encoded repertoire. The core for spans U+4E00–U+9FFF and includes 20,992 characters, supplemented by extension blocks that expand the unified set to over 100,000 ideographs as of Unicode 17.0, including 4,298 additions in Extension J. Within this repertoire, the Ideographic Variation Database (IVD) registers IVS for over 13,000 base characters, primarily from collections like Adobe-Japan1 (14,684 sequences for Japanese glyph variants) and Hanyo-Denshi (13,045 sequences tailored to Japanese typography). These sequences pair a base ideograph with one of 240 ideographic variation selectors (U+E0100–U+E01EF) to invoke specific forms, supporting interoperability across fonts and systems. Examples illustrate the practical role of IVS in distinguishing subtle differences. For instance, the base ideograph U+6B4C (歌, meaning "") paired with U+E0100 selects a Japanese-specific variant glyph, reflecting styling. Similarly, regional mappings address variations like those for U+8FBB (貫) in versus contexts, where IVS resolves form discrepancies in traditional Chinese . Such sequences ensure culturally appropriate rendering, particularly in multilingual documents. IVS are vital for accurate East Asian typography, where glyph choice affects readability and cultural fidelity in publishing, legal texts, and digital interfaces. They integrate with standards like CNS 11643, Taiwan's comprehensive character set encompassing over 80,000 ideographs across multiple planes, many of which serve as sources for registered variants to facilitate cross-standard compatibility. Key challenges involve ambiguity resolution within the unified repertoire, as a single code point may correspond to multiple incompatible glyphs across CJK regions, requiring IVS to disambiguate intent. Additionally, non-unified variants—those outside the core unified set—depend heavily on IVD registration for standardization, with ongoing submissions ensuring evolving support but demanding rigorous review to maintain stability.

Emoji and Symbols

Variant forms in Unicode play a crucial role in and symbols by allowing users to specify presentation styles, toggling between colorful representations and monochrome text styles, or selecting particular variants for compatibility. This mechanism ensures that symbols can adapt to contextual needs, such as emphasizing visual expressiveness in messaging or maintaining a neutral, typographic appearance in documents. The use of variation selectors for and symbols evolved significantly starting with Unicode 6.0 in 2010, which introduced initial support for emoji characters, and was further refined in Unicode 6.1 in 2012 with the formal definition of variation sequences. Variation Selector-15 (VS15, U+FE0E) requests a text presentation, rendering the preceding character in a monochrome, outline style suitable for environments, while Variation Selector-16 (VS16, U+FE0F) requests an presentation, displaying it in full color with graphical embellishments. These selectors are non-printing and invisible, applying only to compatible base characters, and their adoption has standardized how platforms handle stylistic variations. Standardized variation sequences dominate this domain, particularly for characters in blocks like Emoticons (U+1F600–U+1F64F), Dingbats (U+2700–U+27BF), and (U+2600–U+26FF). For instance, the grinning face (U+1F600 followed by U+FE0F) renders as a colorful 😀, whereas U+1F600 followed by U+FE0E appears as a simple black-and-white outline. Similarly, the sign (U+00A9 followed by U+FE0E) displays in text style as © (monochrome), contrasting with U+00A9 followed by U+FE0F for an emoji-style version with potential color and shading. These sequences are explicitly listed in 's emoji-variation-sequences.txt file to guide implementers on supported combinations. The impact of these variant forms extends to rendering consistency across diverse platforms and devices, where default styles might vary without explicit selectors, ensuring predictable visual outcomes in global communication. They are also vital for , as screen readers and assistive technologies can ignore the selectors while using associated Common Locale Data Repository (CLDR) annotations to describe the content accurately, aiding users who rely on audio feedback.

Other Scripts

Variant forms in non-CJK and non-emoji scripts employ variation selectors in targeted ways to address glyph alternatives for mathematical styling, orthographic disambiguation, and historical representations, though such usage remains far less extensive than in ideographic systems. These applications primarily leverage the general Variation Selectors (VS1 through VS16, U+FE00–U+FE0F) for compatibility and style specification, with Mongolian featuring dedicated Free Variation Selectors (FVS1–FVS3, U+180B–U+180D). Ideographic Variation Sequences (IVS) are rarely, if ever, applied outside of Han ideographs, confining their role to CJK contexts. In mathematical notations, variation selectors enable precise control over glyph styles within blocks like (U+1D400–U+1D7FF) and Mathematical Operators (U+2200–U+22FF). For example, certain mathematical script capital letters can be modified for chancery or roundhand variants using VS1 (U+FE00) or VS2 (U+FE01), such as the sequence U+1D49C U+FE00 for a chancery-style script A (𝒜). These distinctions aid in denoting variables or functions with consistent typographic emphasis. The Arabic Mathematical Alphabetic Symbols block (U+1EE00–U+1EEFF) provides precomposed bold, italic, and stretched variants of letters for equations, but lacks widespread VS integration, relying instead on fixed code points for presentation forms. The utilizes its specialized FVS to resolve ambiguities in joining and orthographic traditions, supporting both traditional and modern variants across isolate, medial, and final positions. A representative sequence is U+1820 U+180B, which selects the second form of the Mongolian letter A (ᠠ) for specific contextual rendering, ensuring accurate depiction in vertical traditional texts. This mechanism, distinct from the general VS, highlights Mongolian's unique needs for substitution without altering semantics. Historical scripts demonstrate niche applications of VS for positional or rotational adjustments. In the Egyptian Hieroglyphs block (U+13000–U+1342F), VS1 through VS7 specify non-semantic rotations (e.g., 90° clockwise via U+FE00), as in U+13000 U+FE00 for a rotated basic biliteral sign, facilitating faithful reproduction of ancient inscriptions. Such sequences are standardized for over 100 hieroglyphs to accommodate archaeological and epigraphic variations. The Phaistos Disc symbols (U+101D0–U+101FF) represent an undeciphered Minoan artifact but do not employ VS, instead using discrete code points for their 45 distinct ideogram-like signs without registered variants. For legacy compatibility, the Small Form Variants block (U+FE50–U+FE6B) includes small-scale and symbols, such as the small (U+FE50, ﹐), encoded as compatibility equivalents to support the Chinese National Standard (CNS) 11643 without relying on VS; these serve orthographic roles in East Asian but extend to broader script mixing. VS1–VS16 further bolster compatibility in these scripts by allowing fallback selection in fonts lacking full support, though adoption remains sporadic outside specialized domains.

Technical Aspects

Encoding and Registration

Variation sequences in Unicode are formed by a base character immediately followed by a variation selector (VS), typically VS1 through VS16 for standardized variants or VS17 through VS256 for ideographic variants, and are encoded as consecutive s within the text stream. In encoding, each is represented by 1 to 4 bytes depending on its value, ensuring variable-length representation for efficiency, while in UTF-16, code points are encoded using 2 bytes for the Basic Multilingual Plane or surrogate pairs (4 bytes total) for supplementary planes. This structure allows variation sequences to function as single logical units without altering the underlying byte stream structure. These sequences are preserved intact under Unicode normalization forms, including NFC (Normalization Form Canonical Composition) and NFD (Normalization Form Canonical Decomposition), because variation selectors are classified as nonspacing marks that do not participate in canonical decomposition or composition processes. As a result, normalization does not alter or remove the variation selector, maintaining the intended glyph variant distinction even after text processing. The registration of ideographic variation sequences (IVS) occurs through the Unicode Consortium's Ideographic Variation Database (IVD), as detailed in Unicode Technical Standard #37. Interested parties, such as font vendors or organizations like (via its MSARG collection), submit proposed collections by creating a descriptive , announcing the submission on the Unicode public review issues list for a minimum 90-day review period, and providing representative charts to demonstrate the variants. Upon approval by the IVD registrar, the collection receives a , and the approved sequences—each pairing a base ideograph with a specific VS—are incorporated into the IVD, ensuring standardized . The most recent IVD version, released on 2025-07-14, includes updates such as the new CAAPH collection with 198 sequences. Validation of IVS relies on official Unicode data files, including the IVD collection files and StandardizedVariants.txt, which list all registered and standardized sequences for compliance checking; these can be processed with custom tools or scripts to verify submissions against the database. code charts provide visual representations of registered IVS, aiding in review and implementation. For standards conformance, processes must recognize and interpret both standardized variation sequences (defined in the Unicode Character Database) and registered IVS as single units, with normalization handling preserved per Unicode Standard Annex #15 to avoid unintended alterations.

Rendering and Font Support

The rendering of variant forms in Unicode relies on variation sequences, consisting of a base character followed by a variation selector (VS), which specify alternate glyphs for display. Fonts supporting these sequences map the combination to appropriate glyphs through tables, such as the cmap format 14 subtable for ideographic variation sequences (IVS) or GSUB lookups and features like 'cv' (character variants) and 'ss' (stylistic sets) for standardized variants. If the font lacks support for the sequence, rendering engines ignore the VS—classified as default ignorable code points—and display the base character as a fallback, potentially with optional visual indicators like underlining in debugging modes. Major operating systems integrate variation sequence rendering into their text engines, requiring compatible fonts for full functionality. Windows' Uniscribe processes VS by querying font tables for glyph substitutions, including support for IVS via cmap extensions. macOS's Core Text similarly handles these sequences, applying variants when defined in the font's layout data. On mobile platforms like Android, support is partial, with robust handling for VS (e.g., VS16 for emoji style) but inconsistencies for IVS in CJK rendering due to font and engine limitations. Challenges in rendering arise from uneven font coverage and system behaviors. Many fonts exhibit inconsistent IVS support; for example, Noto Sans CJK includes variants from specific collections like KRName for Korean ideographs but omits others, leading to fallback rendering in unsupported cases. Variation selectors are also disregarded in plain text operations such as searching and sorting, where sequences normalize to the base character, potentially causing mismatches in applications relying on exact text matching. Legacy systems or outdated fonts often fail entirely, as they lack recognition of advanced tables like cmap format 14. Testing variation sequence rendering can be performed using specialized tools, such as browser-based tests or utilities in libraries like FreeType. Common failure examples include pre-Unicode 3.2 systems ignoring VS entirely or browsers on older Android versions defaulting to text-style emojis despite VS16 specification. Ongoing advancements in Unicode 17.0 and later versions enhance IVS integration by registering additional standardized variation sequences—such as 42 for rotated Egyptian Hieroglyphs and others for Sibe script—promoting better font implementations and cross-platform consistency.
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