When we deliver our project to you, we provide you with a source code documentation, which details the structure of the code right down to every class and function. Along with this, we also provide you with a code document in PHPDoc format.
This goes hand in hand with our belief that once you purchase a solution from us, you should not be dependent on us. While we do love and appreciate your patronage, and would love to have you come back to us for every software requirement that you have, we stress that you do so because you love our work, and not because you are compelled to do so.
Hence, while many software development companies deliver source code with zero or no documentation, making it impossible for the client to engage a different development team if needed, we do not walk that path. We provide documentation for free with every project, in a widely accepted format, which any developer can understand.
Thus, if you stop loving our work, or we get abducted by an alien race after making your software, do not worry. The work we have done for you will still be useful and can be used as a base by any good development company to develop your project further.