Here is a list of all documented files with brief descriptions:

lzma
base.h	Data types and functions used in many places in liblzma API
bcj.h	Branch/Call/Jump conversion filters
block.h	.xz Block handling
check.h	Integrity checks
container.h	File formats
delta.h	Delta filter
filter.h	Common filter related types and functions
hardware.h	Hardware information
index.h	Handling of .xz Index and related information
index_hash.h	Validate Index by using a hash function
lzma12.h	LZMA1 and LZMA2 filters
stream_flags.h	.xz Stream Header and Stream Footer encoder and decoder
version.h	Version number
vli.h	Variable-length integer handling
lzma.h	The public API of liblzma data compression library