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

thai
thailib.h	General declarations for libthai
thbrk.h	Thai word segmentation
thcell.h	Thai string cell custering
thcoll.h	Thai string collation
thctype.h	Thai character classifications
thinp.h	Thai string input sequence filtering
thrend.h	Thai string rendering
thstr.h	Thai string manipulators
thwbrk.h	Thai wide-char word segmentation
thwchar.h	Wide char support for Thai
thwcoll.h	Thai wide-char string collation
thwctype.h	Thai wide-char character classifications
thwstr.h	Thai wide-char string manipulators
tis.h	TIS-620 character names
wtt.h	WTT I/O implementation