Miscellaneous Binary Properties

Bidi Controls

The Bidi_Control property enumerates formatting characters that serve special functions in the Unicode Bidirectional Algorithm. They include implicit controls which are simply invisible, standalone marks with the same bidi properties as regular letters for lightweight formatting, and explicit controls which are stateful and affect the bidi handling of entire text runs.

Dashes

The Dash property includes all characters with the General_Category property value Dash_Punctuation, plus a few other symbols of a similar nature.

Emoji Modifiers

Emoji modifiers are used in conjuction with emoji modifier bases to produce emoji modifier sequences, which are variants of human‐form emoji with specific skin tones. They employ the Fitzpatrick scale, a six‐point scale that classifies human skin based on its susceptibility to sunburn. Fitzpatrick types I and II have been combined into a single emoji modifier.

See Unicode Technical Standard #51: Unicode Emoji, section 2.4: Diversity for more information.

Emoji Modifier Bases

Emoji modifier bases are all characters that an emoji modifier can be applied to. An emoji modifier sequence always consists of a character with Emoji_Modifier_Base followed immediately by a character with Emoji_Modifier. The “Example” column shows all such combinations for each character. Emoji modifiers automatically request emoji‐style display for their bases, so Variation Selector-16 is not required even for text‐default characters.

Not all well‐formed emoji modifier sequences are recommended for general interchange (RGI). In particular, applications are not expected to support skin tone variants of U+1F46A 👪 Family.

Source: emoji-sequences.txt

Extenders

The set of characters with the Extender property unifies several disparate concepts that are of relevance to the Unicode Collation Algorithm. It includes characters that graphically extend or modify the shape of surrounding characters, as well as extenders in a linguistic sense, such as vowel or consonant lengtheners and repetition marks.

IDS Operators

Ideographic Description Sequences (IDS) are used to describe the shapes of Han, Tangut, Khitan, and Nüshu characters in terms of their components. So‐called ideographic characters are often modular in nature and can be recursively deconstructed into basic radicals and strokes. This is useful both for indexing and categorising these large sets of characters, and for systematically substituting as‐of‐yet unencoded ideographs.

Ideographic description characters represent simple spatial arrangements of ideographic components. They possess one of three properties based on how many operands they take: IDS_Unary_Operator, IDS_Binary_Operator or IDS_Trinary_Operator. Such an operand may in turn be another IDS. The “Example” column shows one Han character separated into its top‐level components for each operator.

See The Unicode Standard, section 18.2: Ideographic Description Characters for more information.

Join Controls

Only two characters possess the Join_Control property: U+200D causes its neighboring characters to form a ligature or assume contextual glyphs as if they were cursively joined to each other even if they otherwise wouldn’t; U+200C prevents ligation or cursive joining of its neighbors.

Logical Order Exception

Unicode text is generally encoded in logical order, also called phonetic order. This means that user‐perceived characters are constructed in such a way that their component code points are placed roughly in the same order as they would be pronounced, even if their visual appearance would suggest a different order. For example, the Devanagari syllable ki (कि) is produced by putting the consonant ka (क) first and the vowel i (◌ि) second in the character stream, even though visually the vowel sign comes before the base consonant with regard to the writing direction.

For various historical reasons, the Thai, Lao, New Tai Lue, and Tai Viet scripts are an exception to this rule. In those scripts, the vowel signs that visually sit to the left of their base consonants actually precede them in the character stream as well. For example, the Thai syllable ke (เก) is written as e (เ) followed by ka (ก).

This poses unique challenges to search and collation algorithms as they need to internally swap such sequences around to process them correctly, which is why all affected characters have been collected in the Logical_Order_Exception property set.

Modifier Combining Marks

Unicode Technical Report #53, Unicode Arabic Mark Rendering uses the Modifier_Combining_Mark property to identify combining characters in the Arabic script that need to be rendered close to their base character regardless of the placement and canonical order of other marks within the same grapheme cluster.

Prepended Concatenation Marks

The Prepended_Concatenation_Mark property identifies formatting characters that, in a sense, are the opposite of combining marks. Whereas combining marks are placed after the base character they modify, prepended concatenation marks are placed before a sequence of characters (usually numerals) they apply to. Most prepended marks require complex rendering, as their glyphs are expected to stretch over or under a run of characters of arbitrary length.

The “Example” column shows each prepended mark applied to a simple sequence of characters.

Quotation Marks

The Quotation_Mark property should be self‐explanatory. It’s for quotation marks.

Soft Dotted

Letters with the Soft_Dotted property include a tittle in their glyph that disappears when a diacritical mark placed above is added. The “Example” column shows each soft‐dotted character with U+0301 ◌́ Combining Acute Accent. Notice how the acute accent completely replaces the tittle from the original base glyph.

White Space

White space characters are often used to separate text elements and generally have no graphic appearance of their own, except for an advance width. The White_Space property includes everything with a General_Category value of Separator, plus a few control characters that have space‐like properties or induce line breaks.