Here are the data structures with brief descriptions:

C_SquashObject	Reference-counting base class for other types
C_SquashOptionInfoEnumStringMap	An item in a map of strings to integer values
C_SquashStreamPrivate	Private data for streams
CSquashCodec	A compression/decompression codec
CSquashCodecImpl	Function table for plugins
CSquashContext	Context for all Squash operations
CSquashOptionInfo	Information about options which can be passed to a codec
CSquashOptionInfoEnumInt	A list of potential integer values
CSquashOptionInfoEnumString	A list of strings which are mapped to integer values
CSquashOptionInfoRangeInt	A range of potential integer values
CSquashOptionInfoRangeSize	A range of potential size values
CSquashOptions	A set of compression/decompression options
CSquashOptionValue	A value
CSquashPlugin	A plugin
CSquashStream	Compression/decompression streams