Cannot convert ECMASCRIPT_2018 feature "RegExp unicode property escape"

[haraleib]

I wonder if there is a reason why google closure-compiler can't convert the following snippet while Babel can do it. (Snippet available with the links below)

Maybe somebody can help me out here or have some input concerning this issue.

Google closure-compiler: https://closure-compiler.appspot.com/home#code%3D%252F%252F%2520%253D%253DClosureCompiler%253D%253D%250A%252F%252F%2520%2540compilation_level%2520SIMPLE_OPTIMIZATIONS%250A%252F%252F%2520%2540output_file_name%2520default.js%250A%252F%252F%2520%253D%253D%252FClosureCompiler%253D%253D%250A%250A%252F%252F%2520ADD%2520YOUR%2520CODE%2520HERE%250Afunction%2520proper(ast%252C%2520state)%2520%257B%250A%2520%2520%2520%2520return%2520this.runFunction(ast.args%252C%2520state%252C%2520this.metadata('PROPER')%252C%2520arg%2520%253D%253E%2520%257B%250A%2520%2520%2520%2520%2520%2520return%2520arg.replace(%252F%255Cp%257BL%257D%252B%252Fgu%252C%2520word%2520%253D%253E%2520word.charAt(0).toUpperCase()%2520%252B%2520word.substring(1).toLowerCase())%253B%250A%2520%2520%2520%2520%257D)%253B%250A%257D%250A%250A,

Babel: https://babeljs.io/repl#?browsers=&build=&builtIns=false&corejs=3.21&spec=false&loose=false&code_lz=GYVwdgxgLglg9mABABwE52QU1QCgIYDOUANIkXlJgJSIDeAUIk4qplCKklABYwEB0qcADFw0eGHxF-eVAHMCpcpVI8-_ALZs8AEwp4cAcgAKAJQDyxgKKnDVUrLmIAvAD46jZk1btOiR4KYyAA2eBCYOAD0ADrItAAyAL4A1JFyIKQA7nCoOi7u2bn8ENyyAIJQOAAMVPxQcACqyFioAMKEETTJiIU6_AQgAEZEqDBgcjgAjLX18XCZ2O0EnVQA3J5MiWv0iUA&debug=false&forceAllTransforms=false&modules=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=env%2Cstage-2&prettier=false&targets=&version=7.22.17&externalPlugins=&assumptions=%7B%7D