Inhibitor connections can prevent a element from firing. An inhibitor checks if another element contains a specific number of resources, if not the original element cannot fire. There are two type of inhibitors, inhibitors that actually consume resources and inhibitors that do not. The latter are called state inhibitors and are represented with dotted lines.
When creating an inhibitor you can set the end value to determine how many resources another element must contain in order to fire the first element.
State inhibitors can have start value of 0, in which case the inhibition is 'inversed': the element is inhibited when the linked element has 1 or more resources but it can fire when the linked element has 0 resources.
When editing an inhibitor, select it to see and drag its (square) connection points. Drag a connection point over an element to attach it to that element.
Drag the green circle to create a waypoint for a curved inhibitor.