what is the axis of a gradient?

A draw:gradient has among others the attributes draw:angle and draw:style.

One possible value for draw:style is "linear", this is defined as: " a gradient where the colors blend along a linear vector perpendicular to the axis of the gradient."

If the colors blend along a vector perpendicular to the axis, then along the axis, the color should be constant, but the definition of draw:angle is:
"The draw:angle attribute specifies an angle that rotates the axis at which the gradient values are interpolated. " So apparently the colours are interpolated along the axis, not perpendicular to it.

This is a conflict.

Once again of course, we do not specify whether the angle is given in mathematically positive (ie. counter clockwise) sense and where the 0 degree axxis is.