Spiegeleigenschaft

What Is the Bidi_Mirrored Property?

The Bidi_Mirrored property is a Boolean property that marks characters whose glyph should be horizontally reflected when appearing in a right-to-left (RTL) context. In an RTL paragraph, an opening parenthesis ( should visually appear as ) and vice versa, because the semantic role (open vs. close) is independent of whether the text flows left-to-right or right-to-left.

The Unicode Bidirectional Algorithm (UAX #9) applies mirroring automatically during text rendering for characters with Bidi_Mirrored=Yes. A rendering engine does not swap code points; instead it selects the mirrored glyph from the font, or uses the Bidi_Mirroring_Glyph property to find the corresponding code point when a dedicated glyph is not available.

Characters with Bidi_Mirrored=Yes

The most familiar mirrored characters are paired delimiters, but the property covers a wider range:

import unicodedata

# Check Bidi_Mirrored flag (1 = mirrored, 0 = not mirrored)
candidates = [
    ("(", "LEFT PARENTHESIS"),
    (")", "RIGHT PARENTHESIS"),
    ("[", "LEFT SQUARE BRACKET"),
    ("{", "LEFT CURLY BRACKET"),
    ("<", "LESS-THAN SIGN"),
    (">", "GREATER-THAN SIGN"),
    ("⟨", "MATHEMATICAL LEFT ANGLE BRACKET"),
    ("∈", "ELEMENT OF"),
    ("A", "LATIN CAPITAL LETTER A"),
]

for char, name in candidates:
    m = unicodedata.mirrored(char)
    print(f"  {char}  mirrored={m}  {name}")

# (  mirrored=1  LEFT PARENTHESIS
# )  mirrored=1  RIGHT PARENTHESIS
# [  mirrored=1  LEFT SQUARE BRACKET
# {  mirrored=1  LEFT CURLY BRACKET
# <  mirrored=1  LESS-THAN SIGN
# >  mirrored=1  GREATER-THAN SIGN
# ⟨  mirrored=1  MATHEMATICAL LEFT ANGLE BRACKET
# ∈  mirrored=1  ELEMENT OF
# A  mirrored=0  LATIN CAPITAL LETTER A

Bidi_Mirroring_Glyph vs. Bidi_Mirrored

Bidi_Mirrored=Yes says this character needs mirroring. The companion Bidi_Mirroring_Glyph property gives the code point of the character whose glyph should be used as the mirrored form—for example, ( → ). For mathematical symbols like ∈ (ELEMENT OF), the mirroring glyph is ∋ (CONTAINS AS MEMBER). If a font contains both glyphs, the renderer selects the appropriate one automatically.

When no mirroring glyph exists (the value is <none> in the data), the renderer must synthesize a mirrored glyph, typically by applying a horizontal flip transformation.

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