liblouis: Character-Class Opcodes

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1 2.9 Character-Class Opcodes
1 ===========================
1 
1 These opcodes define and use character classes.  A character class
1 associates a set of characters with a name.  The name then refers to any
1 character within the class.  A character may belong to more than one
1 class.
1 
1    The basic character classes correspond to the character definition
11 opcodes, with the exception of the 'uplow' opcode (⇒uplow uplow
 opcode.), which defines characters belonging to the two classes
1 'uppercase' and 'lowercase'.  These classes are:
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1 'space'
1      Whitespace characters such as blank and tab
1 'digit'
1      Numeric characters
1 'letter'
1      Both uppercase and lowercase alphabetic characters
1 'lowercase'
1      Lowercase alphabetic characters
1 'uppercase'
1      Uppercase alphabetic characters
1 'punctuation'
1      Punctuation marks
1 'sign'
1      Signs such as percent ('%')
1 'math'
1      Mathematical symbols
1 'litdigit'
1      Literary digit
1 'undefined'
1      Not properly defined
1 
1    The opcodes which define and use character classes are shown below.
1 For examples see 'fr-abrege.ctb'.
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1 'class name characters'
1      Define a new character class.  The characters operand must be
1      specified as a string.  A character class may not be used until it
1      has been defined.
1 
1 'after class opcode ...'
1      The specified opcode is further constrained in that the matched
1      character sequence must be immediately preceded by a character
1      belonging to the specified class.  If this opcode is used more than
1      once on the same line then the union of the characters in all the
1      classes is used.
1 
1 'before class opcode ...'
1      The specified opcode is further constrained in that the matched
1      character sequence must be immediately followed by a character
1      belonging to the specified class.  If this opcode is used more than
1      once on the same line then the union of the characters in all the
1      classes is used.
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