src/vs/workbench/services/extensions/common/abstractExtensionService.ts/ProposedApiController/updateEnableProposedApi
class ProposedApiController:	public updateEnableProposedApi(extension: IExtensionDescription): void {
		if (this._allowProposedApiFromProduct(extension.identifier)) {
			// fast lane -> proposed api is available to all extensions
			// that are listed in product.json-files
			extension.enableProposedApi = true;

		} else if (extension.enableProposedApi && !extension.isBuiltin) {
			if (
				!this.enableProposedApiForAll &&
				this.enableProposedApiFor.indexOf(extension.identifier.value.toLowerCase()) < 0
			) {
				extension.enableProposedApi = false;
				console.error(`Extension '${extension.identifier.value} cannot use PROPOSED API (must started out of dev or enabled via --enable-proposed-api)`);

			} else if (this._environmentService.isBuilt) {
				// proposed api is available when developing or when an extension was explicitly
				// spelled out via a command line argument
				console.warn(`Extension '${extension.identifier.value}' uses PROPOSED API which is subject to change and removal without notice.`);
			}
		}
	}