Editing Code on demand (section)

=== Code on demand ===
Code on demand (COD) is the only optional constraint in REST. It allows clients to improve their flexibility because it is the server which decides how certain things will be done. For instance, with code on demand, a client can download a Javascript, Java applet or even a Flash application in order to encrypt communication so servers are not aware of any encryption routines / keys used in this process.{{Clarify|date=June 2024}}

However, using COD reduces visibility, hence the optionality. Also, not every API needs this kind of flexibility.