While the function StringPropertyReplacer#replaceProperties describes nicely how the replacements work, there is nothing about this in the docs. 

https://github.com/infinispan/infinispan/blob/1e7ab8a134e791c50ae859797b5d33fa2e0ff511/commons/all/src/main/java/org/infinispan/commons/util/StringPropertyReplacer.java#L52-L72

Especially useful for the Keycloak project was it to learn that environment variables need to be prefixed by "env."