Some input properties require only a single input to define their value. For example, when creating a Line.ByStartPointDirectionLength, each parameter accepts as few as one input, such as point01 for the StartPoint, plane01 for the Direction, and 3.65 for the Length.

Clicking in the input field allows you to fill in the input values.

In this example StartPoint is the name of the Input property. IPoint stands for the type of input that is possible for this particular input. In this case, anything that implements the IPoint interface can be used as an input for the StartPoint. A point, a coordinate system, and a plane implement the IPoint interface and can be used interchangeably (as does a line's start or end point – line01.EndPoint). The text "(repl.)" signifies that either a single input value (like a single point) or a list of nodes can be used. Similarly, Direction implements the IDirectionOrPoint interface. Therefore any direction, line, curve, point, plane, or coordinate system is an acceptable input.