There are several aspects to the quality of a piece of software. Aside from external issues, such as ``How easy is it to use?'', the quality issues internal to the programming activity include the following:
If quality in this respect is low then nothing else matters, but attention to quality in the following points will contribute to achievement of quality in respect of correctness.
If quality in this respect is low then, even if the program is (mostly) correct, it may be very difficult and/or expensive to maintain (to adapt to new requirements, or to correct faults uncovered during testing or by users).
If the documentation is poor, then even if a program is correct, with appropriate use of language constructs, it may still be so impenetrable that it is difficult and/or expensive to maintain.
5inLet's concentrate on the internal documentation of a program. This is a collection of general observations and thoughts on style in the construction and presentation of the source text of a program.