Create a custom function plug-in in Appian cloud

Hi Appian folks,

I was trying to go through Appian documentation and academy for creating a custom function plug-in. I had a question:

• Trying to import "com.appiancorp.suiteapi.expression.annotations" on IntelliJ for Java class. It is unable to recognize the "com.appiancorp" library. We might need a JAR file for "com.appiancorp" package. I am trying find the JAR file to download but unable to find it. Am I missing anything here?
• Also, is there any other approach that you could suggest to get the appropriate libraries to create a custom plug-in for Appian via. IntelliJ?