In the preferences for IntelliJ 2018.1 (Build, Execution, Deployment > Compiler > Java Compiler) is an checkbox labeled:
Use '--release' option for cross-compilation (Java 9 and later)
I found for information when doing an internet search. The "?" help icon give a 404 error when clicked.
What is the purpose/function of this option?
The help section can be found here:
By default, this option is selected. IntelliJ IDEA deduces from project settings when the cross-compilation is needed and automatically applies the --release compiler option for Java 9.
What is the --release option? It is a new command-line option, defined in JEP 247: Compile for Older Platform Versions.
A new command-line option,
--release, is defined, which automatically configures the compiler to produce class files that will link against an implementation of the given platform version.
Discussed in this good answer here.
Also check IDEA-184333 for the background why this option was added in the IDE. In short, some users need to specify only -source and -target versions for their projects without also setting the -bootclasspath option.