The key factors that assist in creating a maintainable solution are:
A maintainable solution is a solution where any competent IT provider with the technical skills should be able to pick up the source code, understand what it is doing and modify it to solve problems, fix bugs or add features.
Coding standards mean that variables are clearly labelled, their type is obvious as is their purpose. Reading the code is easier as a result.
The modular approach means that bugs only exist in one place and that code can be reused effectively.
Documentation, whether within code or external means that: