Contributed to the matplotlib/matplotlib repository by developing a new API parameter, legend.linewidth, which allows users to customize the edge linewidth of legend boxes for improved visual control in data visualizations. The work involved implementing the parameter in Python, writing comprehensive unit tests to ensure reliability, and addressing linting and mypy issues to maintain code quality and CI stability. Documentation and usage guides were updated to reflect the new feature, supporting developer adoption. Collaboration with a co-author ensured robust code review and adherence to project standards. The contribution focused on enhancing visual consistency while minimizing changes to the existing API surface.