Checks the boundaries of the curve interval and calculates a point from the curve interval that corresponds to the specified coefficient. 

true if and only if the parametric interval of the curve is bounded and the value of the coef variable lies within [0; 1].

The value of the coef variable must be within [0; 1], where:

• 0 is the beginning of the curve interval
• 0.5 is the middle of the curve interval
• 1 is the end of the curve interval