# Section 8.17:
Text Classes

This section of the required library contains definitions of those abstractions and classes which are related to the various forms of text for which this library provides.

1. Abstract Classes

   1. $CHAR - This abstraction encapsulates the notion of a single character - which will contain one or more encodings required to produce the glyph when rendered. A character is thus a logical concept which has semantics which are unrelated to the codes which may be used to represent it.

2. Immutable Classes

   1. CHAR - A single character having only a single glyph encoding.

3. Reference Classes

   1. STR - A string of text with immutable semantics consisting of a sequence of characters each of which only have a single glyph encoding - which is specified as part of the string.
   2. FSTR - A string of text consisting of a sequence of characters each of which only have a single glyph encoding - which is specified as part of the string. This is a class with reference semantics.
   3. STR_CURSOR - A cursor associated with a string buffer providing features for easy scanning.

   4. RUNE - A single character having one or more glyph encodings.
   5. RUNES - A string of text with immutable semantics consisting of a sequence of runes which may individually have any number of encodings - which is specified as part of the string.
   6. FRUNES - A string of text consisting of a sequence of runes which may individually have any number of encodings - which is specified as part of the string.
   7. RUNES_CURSOR - A cursor associated with a runes buffer providing features for easy scanning.

   8. OCT_STR - A string of text with immutable semantics consisting of a sequence of characters each of which has a single 8-bit glyph encoding - which is specified as part of the string.
   9. HEX_STR - A string of text with immutable semantics consisting of a sequence of characters each of which has a single 16-bit glyph encoding - which is specified as part of the string.
   10. QUAD_STR - A string of text with immutable semantics consisting of a sequence of characters each of which has a single 32-bit glyph encoding - which is specified as part of the string.

   11. REG_EXP - an object of this class is an Extended Regular expressions as specified in ISO/IEC 9945-2 Information Technology - Portable Operating System Interface (POSIX) Part 2: Shell and Utilities.

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