Under Animation section:

The animation's parameters define the inputs to the animation: a set of floating point scalar values representing time (the "TIME" input); and sets of three-component floating-point vectors representing translation, rotation, and scale. Each of these inputs is stored in a buffer and accessed via an accessor.

Under sampler.interpolation:

When an animation targets a node's rotation, and the animation's interpolation is "LINEAR", spherical linear interpolation (slerp) should be used to interpolate quaternions.

A couple questions:

• Providing a 3-component Euler angles alone is ambiguous. We're missing the rotation order. Without it you cannot correctly construct the rotation since different engines have different default rotation orders.
• Is it valid to directly store 4-component quaternions for rotation instead? This would solve the ambiguity plus avoid the conversion at runtime. If so, how do we distinguish it from the 3-component Euler rotation? Would it be "VEC4" under accessor.type?