Bug system: https://bugs.openjdk.java.net

JDK-8235497: Add SourceVersion.RELEASE_15
JDK-8227044: javax.lang.model for sealed classes
JDK-8246368: Add override for return tag of Modifier::toString
JDK-8246290: Refine specification of javax.lang.model.element.Modifier::toString
JDK-8245146: Update description of SourceVersion.RELEASE_15 with text blocks
JDK-8244673: Add periods to SourceVersion.isName javadoc
JDK-8240130: Improve and update discussion of visitor evolution warnings
JDK-8239478: Make specification of SourceVersion.isName explicit for dotted names
JDK-8239092: Provide explicit specification for getKind methods of javax.lang.model
JDK-8225495: Note whether returned annotations are declaration annotations or type annotations
JDK-8193553: Provide better guidance on using javax.lang.model visitors