All WEB programs maintain two internal arrays for character transformations.
The first one translates each input character into the internal character
code and the second one does the same in the reverse way if any output is
written to a stream.  By default, each character is mapped to itself in both
directions.

  You can change these two tables at runtime if you set the environment
variable `TEXMAP' pointing to a file in your directory structure.  It is
named TEXMAP because this feature is only implemented with TeX and BibTeX.
Each line of this file should have two or three columns.  Columns are
separated with spaces and/or tabs (leading and trailing space is ignored,
also empty lines and TeXnical comments).  The first entry is the character
code of your machine and the second entry defines the corresponding internal
code of TeX or BibTeX.  The value of the output key-map defaults to the one
of the first column but you can override it with an additional third code.

  There are four ways for writing character codes.  An integer number is
interpreted as a decimal number, a single quote prefix signals an octal
number and a double quote prefix a hexadecimal number.  Characters can be
used, too, if they are prefixed with a single left quote (well, nothing
new).

  Examples:

	'177	127	"7f
	`a	`b		% A comment.

  Note: The TEXMAP feature is disabled with INITEX.
