Creation: Use the external.CreateMiscObject method. 
Class name: RECT

Example:
var rc = external.CreateMiscObject("RECT");

Rect objects represent the rectangles using two points - usually called upper-left and bottom-right. In this documentation they are often called first and second points (corners) of the rectangle:

All the actions performed by the Rect object's methods are intended to change its coordinates (of the both points) and usually return new Rect object holding the result. Rect objects are accepted as parameters by methods and properties of other objects in the ALPFrame. 

Properties

left  - long integer. X coordinate of the first corner of the rectangle

right  - long integer. X coordinate of the second corner of the rectangle

top  - long integer. Y coordinate of the first point of the rectangle

bottom  - long integer. Y coordinate of the second point of the rectangle

isEmpty  - Returns true if the rectangle is empty (with overlapping first and second corners)

first  - Point, Sets/Gets the Point object that represents the first corner of the rectangle

second  - Point, Sets/Gets the Point object that represents the second corner of the rectangle

Methods

Resize

variable = object.Resize( point_object )
Resizes the rectangle to the size specified by the x and y properties of the passed point object.
Example:
var pt = external.CreateMiscObject("POINT");
pt.x = 100; pt.y = 200;
var rc1 = rc.Resize(pt);
Makes the rectangle size 100x200.

Move 

variable = object.Move( point_object )
Moves the rectangle by point_object.x and point_object.y. point_object is a previously created Point object.  
Example:
var pt = external.CreateMiscObject("POINT");
pt.x = 100; pt.y = -100;
var rc1 = rc.Move(pt);
Moves the rectangle by +100 on X axis and -100 on Y axis.

Shrink

variable = object.Shrink( point_object )
Shrinks the rectangle by point_object.x and point_object.y. point_object is a previously created Point object.  
Example:
var pt = external.CreateMiscObject("POINT");
pt.x = 20; pt.y = 20;
var rc1 = rc.Shrink(pt);
Reduces the rectangle size by 20 on each side. 

Expand 

variable = object.Expand( point_object )
Expands the rectangle by point_object.x and point_object.y. point_object is a previously created Point object.  
Example:
var pt = external.CreateMiscObject("POINT");
pt.x = 20; pt.y = 20;
var rc1 = rc.Expands(pt);
Enlarges the rectangle size by 20 on each side. 

IsPointInRect

variable = object.Expand( point_object )
Checks if the point_object is in the rectangle and returns true/false to indicate the result. point_object is a previously created Point object.  
Example:
var pt = external.CreateMiscObject("POINT");
var rc = external.CreateMiscObject("RECT");
rc.left = 5; rc.top = 5; rc.right = 100; rc.bottom = 200;
pt.x = 20; pt.y = 20;
var boolResult = rc.IsPointInRect(pt);
The result is true - the point (20,20) is in the rectangle (5,5,100,200). 

IsEqual

variable = object.IsEqual( rect_object )
Compares the both rectangles and returns true if they are equal and false if not.
rect_object is another Rect object.
Example:
var rc1 = external.CreateMiscObject("RECT");
var rc2 = external.CreateMiscObject("RECT");
rc1.left = 5; rc1.top = 5; rc1.right = 100; rc1.bottom = 200;
rc2.left = 10; rc2.top = 5; rc2.right = 100; rc2.bottom = 200;
var boolResult = rc1.IsEqual(rc2);
The result is false.

Intersect

variable = object.Intersect( rect_object )
Returns the new rectangle holding the intersection of the both recangles.  
rect_object is another Rect object.

Empty

object.Empty();
Empties the rectangle - makes all the coordinates 0.

Subtract

variable = object.Subtract( rect_object )
Returns the new rectangle holding the subtraction of the both recangles.  
rect_object is another Rect object.

Union

variable = object.Union( rect_object )
Returns the new rectangle holding the union of the both recangles.  
rect_object is another Rect object.