As a maintainer of an open-source UI library, most challenging requests are not always about performances or bugs. It can also be about customization. This topic is a permanent balance between code maintainability, developer experience, and documentation.

From my experience as React developper at MUI, I will present most of the customization we face, and what are the usual strategies to answer them, and the tradeoff they imply. Allowing you to add customization in your own components or have an overview of how your favorite library manages customization.