JavaFX defines two system properties that identify the version of JavaFX, "javafx.version" and "javafx.runtime.version".

They are defined as follows, using the definitions from JEP 322 [1].

javafx.version : $VNUM(-$PRE)?
javafx.runtime.version : $VNUM(-$PRE)?\+$BUILD(-$OPT)?

VNUM is taken from the "build.properties" file using the "jfx.release.*.version" properties
PRE is taken from the "jfx.release.suffix" property for release builds, or is set to "-internal" for developer builds; for release builds, if MILESTONE_FCS is set "true", then PRE is omitted
(BUILD and OPT are not relevant for this enhancement request)

Examples include:

GA builds:
    javafx.version = 23
    javafx.runtime.version = 23+29
 
EA builds:
    javafx.version = 23-ea
    javafx.runtime.version = 23-ea+19

Developer builds:
    javafx.version = 24-internal
    javafx.runtime.version = 24-internal+0-2024-10-14-130317

We propose a new property in "build.properties" that will be used to identify an early access build of an experimental feature branch rather than from the JavaFX mainline. We need to finalize the name for the new property; the working name is:

jfx.experimental.release.suffix

If "jfx.experimental.release.suffix" is not empty, it will override "jfx.release.suffix". The intention is to use this for experimental builds from a branch in the sandbox. This property should be set in the build.properties file in the sandbox branch to identify the experimental feature. For example, the following would be set in the metal branch of jfx-sandbox:

jfx.experimental.release.suffix=-metal

This would result in the following:

    javafx.version = 23-metal
    javafx.runtime.version = 23-metal+$BUILD

NOTE: Since experimental releases are never GA releases, it is an error to set MILESTONE_FCS=true if "jfx.experimental.release.suffix" is not empty.

[1] https://openjdk.org/jeps/322