Expr: A continuous function. 

AngleOrVector: A vector matrix or an angle. A vector is a one dimensional matrix, either row ([x,y]) or column ([x;y]). It can be the zero vector ([0], [0;0], [0,0,0], etc.). The angle can be in either degrees or radians if the appropriate symbol is used ( ° , ^r ), or in the default unit if no symbol is used, or it can be an undefined variable. 

VarPointList: Must list all variables, {x, y,...}, and may indicate the point of evaluation, {x=Px, y=Py,...}. 

Return value: 
The derivative: If AngleOrVector is a zero vector, [0], or evaluates to a variable, and VarPointList does not include the point. If AngleOrVector is a vector, the derivative will be returned as a vector. 

The gradient: If AngleOrVector is a zero vector, [0], or evaluates to a variable, and VarPointList includes the point. If AngleOrVector is a vector, the gradient will be returned as a vector. 

The directional derivative: If AngleOrVector is an angle or a non-zero vector. 

Examples: 
ANGLE 
1. dd(x2y+xy2,u,{x,y)) Derivative 
     x² sin(u)+2xy(cos(u)+sin(u))+cos(u)y² 

2. dd(x2y+xy2,u,{x=1,y=1)) Gradient 
     3 cos(u)+3 sin(u) 

3. dd(x2y+xy2,pi/3,{x=1,y=1)) Directional derivative 
     3*sqrt(3)/2+3/2 

VECTOR  
1. dd(x2y+xy2,[0],{x,y)) Derivative 
     [2xy+y² , x²+2xy] 

2. dd(x2y+xy2,[0],{x=1,y=1)) Gradient 
     [3 , 3] 

3. dd(x2y+xy2,[1/2 , sqrt(3)/2],{x=1,y=1)) Directional derivative 
     3*sqrt(3)/2+3/2 

4. dd(x2y+xy2-z,[1, 1, 0],{x=1,y=1,z=0)) Directional derivative 
     3*sqrt(2)