Getting java.lang.IllegalArgumentException when setting stri

[gmoh]

I'm getting an IllegalArgumentException when setting a property with a dot in the property name saying it is "not a valid java identifier"
Could someone explain what this means?

[genman]

http://javaalmanac.com/egs/java.lang/IsJavaId.html

[gmoh]

Thanks, why does a property name have to be a java identifier?