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(elisp)Selecting a Representation

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Selecting a Representation
==========================

   Sometimes it is useful to examine an existing buffer or string as
multibyte when it was unibyte, or vice versa.

 - Function: set-buffer-multibyte multibyte
     Set the representation type of the current buffer.  If MULTIBYTE
     is non-`nil', the buffer becomes multibyte.  If MULTIBYTE is
     `nil', the buffer becomes unibyte.

     This function leaves the buffer contents unchanged when viewed as a
     sequence of bytes.  As a consequence, it can change the contents
     viewed as characters; a sequence of two bytes which is treated as
     one character in multibyte representation will count as two
     characters in unibyte representation.  Character codes 128 through
     159 are an exception.  They are represented by one byte in a
     unibyte buffer, but when the buffer is set to multibyte, they are
     converted to two-byte sequences, and vice versa.

     This function sets `enable-multibyte-characters' to record which
     representation is in use.  It also adjusts various data in the
     buffer (including overlays, text properties and markers) so that
     they cover the same text as they did before.

     You cannot use `set-buffer-multibyte' on an indirect buffer,
     because indirect buffers always inherit the representation of the
     base buffer.

 - Function: string-as-unibyte string
     This function returns a string with the same bytes as STRING but
     treating each byte as a character.  This means that the value may
     have more characters than STRING has.

     If STRING is already a unibyte string, then the value is STRING
     itself.  Otherwise it is a newly created string, with no text
     properties.  If STRING is multibyte, any characters it contains of
     charset EIGHT-BIT-CONTROL or EIGHT-BIT-GRAPHIC are converted to
     the corresponding single byte.

 - Function: string-as-multibyte string
     This function returns a string with the same bytes as STRING but
     treating each multibyte sequence as one character.  This means
     that the value may have fewer characters than STRING has.

     If STRING is already a multibyte string, then the value is STRING
     itself.  Otherwise it is a newly created string, with no text
     properties.  If STRING is unibyte and contains any individual
     8-bit bytes (i.e. not part of a multibyte form), they are
     converted to the corresponding multibyte character of charset
     EIGHT-BIT-CONTROL or EIGHT-BIT-GRAPHIC.