All types, procedures, tokens, predefined variables and utility procedures mentioned in this document are required to be present in all C implementations that conform to this specification. The C header file which declares all of these required names, ri.h, is listed in Appendix C, Language Binding Details. A bound is a bounding box and is specified by 6 floating point values in the order xmin, xmax, ymin, ymax, zmin, zmax. A matrix is an array of 16 numbers describing a 4 by 4 transformation matrix. All multidimensional arrays are specified in row-major order.
Tokens are strings that have a special meaning to procedures implementing the interface.
These meanings are described with each procedure. The capabilities of the RenderMan Interface can be extended by defining new tokens and passing them to various procedures. The most important of these are the tokens identifying variables defined by procedures called shaders, written in the Shading Language. Variables passed through the RenderMan Interface are bound by name to shader variables. To make the standard predeclared tokens and user-defined tokens similar, RenderMan Interface tokens are represented by strings.