@code{canonical-combining-class}. However, sometimes we shorten the
names to make their use easier.
+@cindex unassigned character codepoints
+ Some codepoints are left @dfn{unassigned} by the
+@acronym{UCD}---they don't correspond to any character. The Unicode
+Standard defines default values of properties for such codepoints;
+they are mentioned below for each property.
+
Here is the full list of value types for all the character
properties that Emacs knows about:
@item name
Corresponds to the @code{Name} Unicode property. The value is a
string consisting of upper-case Latin letters A to Z, digits, spaces,
-and hyphen @samp{-} characters.
+and hyphen @samp{-} characters. For unassigned codepoints, the value
+is an empty string.
@cindex unicode general category
@item general-category
Corresponds to the @code{General_Category} Unicode property. The
value is a symbol whose name is a 2-letter abbreviation of the
-character's classification.
+character's classification. For unassigned codepoints, the value
+is @code{Cn}.
@item canonical-combining-class
Corresponds to the @code{Canonical_Combining_Class} Unicode property.
-The value is an integer number.
+The value is an integer number. For unassigned codepoints, the value
+is zero.
@cindex bidirectional class of characters
@item bidi-class
Corresponds to the Unicode @code{Bidi_Class} property. The value is a
symbol whose name is the Unicode @dfn{directional type} of the
character. Emacs uses this property when it reorders bidirectional
-text for display (@pxref{Bidirectional Display}).
+text for display (@pxref{Bidirectional Display}). For unassigned
+codepoints, the value depends on the code blocks to which the
+codepoint belongs: most unassigned codepoints get the value of
+@code{L} (strong L), but some get values of @code{AL} (Arabic letter)
+or @code{R} (strong R).
@item decomposition
Corresponds to the Unicode @code{Decomposition_Type} and
brackets; e.g., Unicode specifies @samp{<small>} where Emacs uses
@samp{small}.
}; the other elements are characters that give the compatibility
-decomposition sequence of this character.
+decomposition sequence of this character. For unassigned codepoints,
+the value is the character itself.
@item decimal-digit-value
Corresponds to the Unicode @code{Numeric_Value} property for
characters whose @code{Numeric_Type} is @samp{Digit}. The value is an
-integer number.
+integer number. For unassigned codepoints, the value is @code{nil},
+which means @acronym{NaN}, or ``not-a-number''.
@item digit-value
Corresponds to the Unicode @code{Numeric_Value} property for
characters whose @code{Numeric_Type} is @samp{Decimal}. The value is
an integer number. Examples of such characters include compatibility
subscript and superscript digits, for which the value is the
-corresponding number.
+corresponding number. For unassigned codepoints, the value is
+@code{nil}, which means @acronym{NaN}.
@item numeric-value
Corresponds to the Unicode @code{Numeric_Value} property for
characters that have this property include fractions, subscripts,
superscripts, Roman numerals, currency numerators, and encircled
numbers. For example, the value of this property for the character
-@code{U+2155} (@sc{vulgar fraction one fifth}) is @code{0.2}.
+@code{U+2155} (@sc{vulgar fraction one fifth}) is @code{0.2}. For
+unassigned codepoints, the value is @code{nil}, which means
+@acronym{NaN}.
@cindex mirroring of characters
@item mirrored
Corresponds to the Unicode @code{Bidi_Mirrored} property. The value
-of this property is a symbol, either @code{Y} or @code{N}.
+of this property is a symbol, either @code{Y} or @code{N}. For
+unassigned codepoints, the value is @code{N}.
@item mirroring
Corresponds to the Unicode @code{Bidi_Mirroring_Glyph} property. The
@code{Y} also have @code{nil} for @code{mirroring}, because no
appropriate characters exist with mirrored glyphs. Emacs uses this
property to display mirror images of characters when appropriate
-(@pxref{Bidirectional Display}).
+(@pxref{Bidirectional Display}). For unassigned codepoints, the value
+is @code{nil}.
@item old-name
Corresponds to the Unicode @code{Unicode_1_Name} property. The value
-is a string.
+is a string. For unassigned codepoints, the value is an empty string.
@item iso-10646-comment
Corresponds to the Unicode @code{ISO_Comment} property. The value is
-a string.
+a string. For unassigned codepoints, the value is an empty string.
@item uppercase
Corresponds to the Unicode @code{Simple_Uppercase_Mapping} property.
-The value of this property is a single character.
+The value of this property is a single character. For unassigned
+codepoints, the value is @code{nil}, which means the character itself.
@item lowercase
Corresponds to the Unicode @code{Simple_Lowercase_Mapping} property.
-The value of this property is a single character.
+The value of this property is a single character. For unassigned
+codepoints, the value is @code{nil}, which means the character itself.
@item titlecase
Corresponds to the Unicode @code{Simple_Titlecase_Mapping} property.
@dfn{Title case} is a special form of a character used when the first
character of a word needs to be capitalized. The value of this
-property is a single character.
+property is a single character. For unassigned codepoints, the value
+is @code{nil}, which means the character itself.
@end table
@defun get-char-code-property char propname
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