The Pro Key gives access to some advanced features in ADE.  For many users ADE will provide everything they need to create or enhance airports in both FS9 and FSX.  ADE has been designed to be a user friendly as possible and has a number of mechanisms that reduce the risk of creating an airport that will not compile or that does not work in the Simulator.  Some users will want more control like direct access to the XML code or the ability to move or rotate entire airports.  Pro Key will give access to these and more.

New ProKey are usually added on a regular basis.  Those currently available include:

• Move airport
• Rotate airport
• Edit properties directly ( Raw Data View allows editing of underlying XML)
• Save fault finder options
• Open last saved project when ADE starts
• Custom hide airport objects
• Nudge objects accurately into position with arrow keys
• Specify the number of vertices to be used when creating elliptical helper shapes
• Copy/Paste coordinates between objects
• Re-size helper shapes using handles
• Skip the compile of specific objects
• Conditional compile of different object groups
• Extended default settings for taxi links
• Ignore layer constraints.  ADE draws objects above or below each other based on a set of drawing layers designed to match FS as close as possible.  Sometimes it is convenient for users to ignore these constraints while working on an airport

The ProKey is not free and currently costs $9.99.  You can however download a trial version from here