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 ANSI Common Lisp    2 Syntax    2.1 Character Syntax    2.1.4 Character Syntax Types
2.1.4.5   Multiple Escape Characters
A pair of multiple escape characters
is used to indicate that an enclosed sequence of characters,
including possible macro characters and whitespace2 characters,
are to be treated as alphabetic2 characters 
with case preserved.
Any single escape and multiple escape characters 
that are to appear in the sequence must be preceded by a single escape 
character.  
Vertical-bar is a multiple escape character
in standard syntax.
 2.1.4.5.1  Examples of Multiple Escape Characters
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