code: private boolean verifyProvide(Node methodName, Node arg) {
      if (!verifyLastArgumentIsString(methodName, arg)) {
        return false;
      }
  
      if (!NodeUtil.isValidQualifiedName(
          compiler.getOptions().getLanguageIn().toFeatureSet(), arg.getString())) {
        compiler.report(
            JSError.make(
                arg,
                INVALID_PROVIDE_ERROR,
                arg.getString(),
                compiler.getOptions().getLanguageIn().toString()));
        return false;
      }
  
      return true;
    }
docs: Verifies that a provide method call has exactly one argument, and that it's a string literal
  and that the contents of the string are valid JS tokens. Reports a compile error if it doesn't.
  
  @return Whether the argument checked out okay