Commit af38459f authored by Eli Zaretskii's avatar Eli Zaretskii

(Coding System Basics): Rewrite @ignore'd paragraph to speak about `undecided'.

(Character Properties): Don't explain the meaning of each property; instead,
identify their Unicode Standard names.
parent 6530de7d
2008-12-05 Eli Zaretskii <eliz@gnu.org>
* nonascii.texi (Coding System Basics): Rewrite @ignore'd
paragraph to speak about `undecided'.
(Character Properties): Don't explain the meaning of each
property; instead, identify their Unicode Standard names.
2008-12-02 Glenn Morris <rgm@gnu.org>
* files.texi (Format Conversion Round-Trip): Rewrite format-write-file
......
......@@ -360,95 +360,97 @@ of character properties. In particular, Emacs supports the
Model}, and the Emacs character property database is derived from the
Unicode Character Database (@acronym{UCD}). See the
@uref{http://www.unicode.org/versions/Unicode5.0.0/ch04.pdf, Character
Properties chapter of the Unicode Standard}, for more details about
Unicode character properties and their meaning.
Properties chapter of the Unicode Standard}, for detailed description
of Unicode character properties and their meaning. This section
assumes you are already familiar with that chapter of the Unicode
Standard, and want to apply that knowledge to Emacs Lisp programs.
The facilities documented in this section are useful for setting and
retrieving properties of characters.
In Emacs, each property has a name, which is a symbol, and a set of
possible values, whose types depend on the property. Here's the full
list of character properties that Emacs knows about:
possible values, whose types depend on the property; if a character
does not have a certain property, the value is @code{nil}. Here's the
full list of value types for all the character properties that Emacs
knows about:
@table @code
@item name
The character's canonical unique name. The value of the property is a
string consisting of upper-case Latin letters A to Z, digits, spaces,
and hyphen @samp{-} characters.
This property corresponds to the Unicode @code{Name} property. The
value is a string consisting of upper-case Latin letters A to Z,
digits, spaces, and hyphen @samp{-} characters.
@item general-category
This property assigns the character to one of the major classes, such
as letters, punctuation, and symbols, and its important subclasses.
The value is a symbol whose name is a 2-letter abbreviation. The
first letter specifies the character's major class and the second
letter designates a subclass of that major class.
This property corresponds to the Unicode @code{General_Category}
property. The value is a symbol whose name is a 2-letter abbreviation
of the character's classification.
@item canonical-combining-class
This property classifies combining characters into several classes,
depending on the details of their behavior in sequences of combining
characters. The property's value is an integer number.
Corresponds to the Unicode @code{Canonical_Combining_Class} property.
The value is an integer number.
@item bidi-class
This property specifies character attributes required for correct
display of @dfn{bidirectional text} used by right-to-left scripts,
such as Arabic and Hebrew. The value is a symbol whose name is the
Unicode @dfn{directional type} of the character.
Corresponds to the Unicode @code{Bidi_Class} property. The value is a
symbol whose name is the Unicode @dfn{directional type} of the
character.
@item decomposition
This property defines a mapping from a character to a sequence of one
or more characters that is a canonical or compatibility equivalent to
it. The value is a list, whose first element may be a symbol
representing a compatibility formatting tag, such as @code{<small>};
the other elements are characters that give the compatibility
decomposition sequence.
Corresponds to the Unicode @code{Decomposition_Type} and
@code{Decomposition_Value} properties. The value is a list, whose
first element may be a symbol representing a compatibility formatting
tag, such as @code{small}@footnote{
Note that Emacs strips the @samp{<..>} brackets from the corresponding
Unicode tags; 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.
@item decimal-digit-value
This property specifies a numeric value of characters that represent
decimal digits. The value is an integer number.
Corresponds to the Unicode @code{Numeric_Value} property for
characters whose @code{Numeric_Type} is @samp{Digit}. The value is an
integer number.
@item digit
This property specifies a numeric value of characters that represent
digits, but not necessarily decimal. Examples include compatibility
subscript and superscript digits. The value is an integer number.
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.
@item numeric-value
This property specifies whether the character represents a number.
Examples of characters that do include fractions, subscripts,
Corresponds to the Unicode @code{Numeric_Value} property for
characters whose @code{Numeric_Type} is @samp{Numeric}. The value of
this property is an integer of a floating-point number. Examples of
characters that have this property include fractions, subscripts,
superscripts, Roman numerals, currency numerators, and encircled
numbers. The value is a symbol whose name gives the numeric value;
for example, the value of this property for the character
@code{U+2155} (@sc{vulgar fraction one fifth}) is the symbol
@samp{1/5}.
numbers. For example, the value of this property for the character
@code{U+2155} (@sc{vulgar fraction one fifth}) is @code{0.2}.
@item mirrored
This is a property of characters such as parentheses, which need to be
mirrored horizontally in right to left scripts. The value is a
symbol, either @samp{Y} or @samp{N}.
Corresponds to the Unicode @code{Bidi_Mirrored} property. The value
of this property is a symbol, either @samp{Y} or @samp{N}.
@item old-name
This property's value specifies the name, if any, of the character in
the old version 1.0 of the Unicode Standard. The value is a string.
Corresponds to the Unicode @code{Unicode_1_Name} property. The value
is a string.
@item iso-10646-comment
This character's comment field from the ISO 10646 standard. The value
is a string, or @code{nil} if there's no comment.
Corresponds to the Unicode @code{ISO_Comment} property. The value is
a string.
@item uppercase
If this character has an upper-case equivalent that is a single
character, then the value of this property is that upper-case
equivalent. Otherwise, the value is @code{nil}.
Corresponds to the Unicode @code{Simple_Uppercase_Mapping} property.
The value of this property is a single character.
@item lowercase
If this character has an lower-case equivalent that is a single
character, then the value of this property is that lower-case
equivalent. Otherwise, the value is @code{nil}.
Corresponds to the Unicode @code{Simple_Lowercase_Mapping} property.
The value of this property is a single character.
@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. If a character has a
title-case equivalent that is a single character, then the value of
this property is that title-case equivalent. Otherwise, the value is
@code{nil}.
character of a word needs to be capitalized. The value of this
property is a single character.
@end table
@defun get-char-code-property char propname
......@@ -793,12 +795,10 @@ alternative encodings for the same characters; for example, there are
three coding systems for the Cyrillic (Russian) alphabet: ISO,
Alternativnyj, and KOI8.
@c I think this paragraph is no longer correct.
@ignore
Most coding systems specify a particular character code for
conversion, but some of them leave the choice unspecified---to be chosen
heuristically for each file, based on the data.
@end ignore
Every coding system specifies a particular set of character code
conversions, but the coding system @code{undecided} is special: it
leaves the choice unspecified, to be chosen heuristically for each
file, based on the file's data.
In general, a coding system doesn't guarantee roundtrip identity:
decoding a byte sequence using coding system, then encoding the
......
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