In that vein, "We, The Developers,..." would be doing the heavy lifting in the implementation. Other developers would take the product and use it rather than having to spend time doing extra work in an area they don't necessarily want to be an expert in. The immediate examples that spring to mind, are matrix calculations (used heavily in transformations) and advanced mathematics (vector math, for one). These would be implemented as used in AutoCAD, with Intellisense and documentation to guide the inputs and outputs so the end user wouldn't necessarily know how to calculate the inverse of a 4x4 matrix of doubles but would be familiar with "I need to transform this line so its end points match these two known points"; or not know how to calculate the intersection of a plane and bounded line but be familiar with "I have a 3D face and a line object, where do they intersect?".