Sets a collection that contains the vertex points of a Polyline.
A pair of double values that identifies the initial point of the object.
Subsequent pairs of double values that define additional vertex points of this object.
The  (bracket) characters are not literals; they indicate optional values. The asterisk (*) indicates that any number of points is permitted after the initial X,Y.
The separator in this grammar can be either a space or a comma. You can use a mixture of spaces and commas as separators. The common convention is to use commas between the X and Y and spaces between the points.
Any odd number of double values in a Points value is illegal and will raise either a parser or a run-time error. The number of double values in the string must always be even so that it is evaluated as x,y pairs that define a point.
A set of points is defined through a string syntax, which is enabled by an underlying type converter. There is no object available in the object model for accessing the set of points as a collection. In either script or XAML, Points is write-only; attempting to get the value in script will result in a run-time GetValue error. You set the value by specifying a string. Without a collection object, there is no way to obtain a count in the object model. However, you could parse the string yourself and count separators, or otherwise get a count before you pass the string as input.
As an example of the pointSet grammar, the string "0,0,50,100,100,0" would produce a "V" shaped polyline with its acute angle placed at 50,100.
A single point, such as (0,0), is a valid value, but it will not render anything because you need a minimum of two points to produce rendered output.