MzScheme's input parser follows these non-standard rules:
Character constants can also be specified through direct ASCII values in octal notation: #\n n n where n is in the range [0, 3] and n and n are in the range [0, 7]. Whenever #\ is followed by at least two characters in the range [0, 7], the next character must also be in this range and the resulting octal number must be in the range to .
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In addition, an identifier cannot start with a hash mark (``#'') unless the hash mark is immediately followed by a percent sign (``%''). The only other special characters are backslash (``\'') or quoting vertical bars (``|''); any other character is used as part of an identifier.
Symbols containing special characters (including delimiters) are expressed using an escaping backslash (``\'') or quoting vertical bars (``|''):
An input token constructed in this way is an identifier when it is not a numerical constant (following the extended number syntax described in section 4.3). A token containing a backslash or vertical bars is never treated as a numerical constant.
Examples:
Whether a vertical bar is used as a special or normal symbol character is controlled with the read-accept-bar-quote Boolean parameter (see section 9.4.1.3). Vertical bar quotes are enabled by default.