if (isLegacyMode()) { // Use legacy code or settings } else { // Use modern code or settings }In this code example, isLegacyMode is called to determine which code or settings to use based on the current environment. If the environment is running in legacy mode, the legacy code or settings are used. Otherwise, the modern code or settings are used. The isLegacyMode function is not part of any specific package or library as it is part of the core PHP functionality.