The contrib category holds components contributed directly by McStas users, rather than authored and maintained by the core McStas team. The McStas team provides the same technical support for these as for any other component, but the original authors – credited individually in each component’s source header and reproduced below – carry primary responsibility for the underlying physics and its validation. Contributed components that mature and see wide use are periodically promoted into a core category (sources, optics, samples, monitors); several components documented in earlier chapters of this manual (e.g. several guide, chopper and polarisation components) began their life in contrib. Always check with mcdoc rather than an older document for a component’s current category.