A translation table is a char-table (see Char-Tables) that specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems.
A translation table has two extra slots. The first is either
nil or a translation table that performs the reverse
translation; the second is the maximum number of characters to look up
for translating sequences of characters (see the description of
make-translation-table-from-alist below).
This function returns a translation table based on the argument
translations. Each element of translations should be a
list of elements of the form (from . to); this says
to translate the character from into to.
The arguments and the forms in each argument are processed in order, and if a previous form already translates to to some other character, say to-alt, from is also translated to to-alt.
During decoding, the translation table’s translations are applied to
the characters that result from ordinary decoding. If a coding system
has the property :decode-translation-table, that specifies the
translation table to use, or a list of translation tables to apply in
sequence. (This is a property of the coding system, as returned by
coding-system-get, not a property of the symbol that is the
coding system’s name. See Basic Concepts of
Coding Systems.) Finally, if
standard-translation-table-for-decode is non-nil, the
resulting characters are translated by that table.
During encoding, the translation table’s translations are applied to
the characters in the buffer, and the result of translation is
actually encoded. If a coding system has property
:encode-translation-table, that specifies the translation table
to use, or a list of translation tables to apply in sequence. In
addition, if the variable standard-translation-table-for-encode
is non-nil, it specifies the translation table to use for
translating the result.
This is the default translation table for decoding. If a coding
system specifies its own translation tables, the table that is the
value of this variable, if non-nil, is applied after them.
This is the default translation table for encoding. If a coding
system specifies its own translation tables, the table that is the
value of this variable, if non-nil, is applied after them.
Self-inserting characters are translated through this translation table before they are inserted. Search commands also translate their input through this table, so they can compare more reliably with what’s in the buffer.
This variable automatically becomes buffer-local when set.
This function returns a translation table made from vec that is
an array of 256 elements to map bytes (values 0 through #xFF) to
characters. Elements may be nil for untranslated bytes. The
returned table has a translation table for reverse mapping in the
first extra slot, and the value 1 in the second extra slot.
This function provides an easy way to make a private coding system
that maps each byte to a specific character. You can specify the
returned table and the reverse translation table using the properties
:decode-translation-table and :encode-translation-table
respectively in the props argument to
define-coding-system.
This function is similar to make-translation-table but returns
a complex translation table rather than a simple one-to-one mapping.
Each element of alist is of the form (from
. to), where from and to are either characters or
vectors specifying a sequence of characters. If from is a
character, that character is translated to to (i.e., to a
character or a character sequence). If from is a vector of
characters, that sequence is translated to to. The returned
table has a translation table for reverse mapping in the first extra
slot, and the maximum length of all the from character sequences
in the second extra slot.