Harbour is a cross-platform compiler for the xBase superset language often referred to as Clipper (the language that is implemented by the compiler CA-Clipper).
The purpose of this manual is basically how to use the different components of the language and important extensions rather than mere as a function reference. Because Harbour is 100% Clipper compatible on language level the documentation of which can be found in Clipper Norton Guides. Also you can refer to very fine help manual published by xHarbour.com.
However it is possible that this manual can diversify to other topics which may be considered important.
To start with I will cover GTWVG in specific and GTWVT in general.
Please note that whenever "Harbour" is refered it will imply both compilers Harbour as well as xHarbour. If a reference to either compiler is necessary it will be mentioned explicitly.