code: public static boolean isVariableName(final String expression) {
          if (expression == null || expression.length() == 0) {
              return false;
          }
  
          if (expression.startsWith(Citrus.VARIABLE_PREFIX) && expression.endsWith(Citrus.VARIABLE_SUFFIX)) {
              return true;
          }
  
          return false;
      }
docs: Checks whether a given expression is a variable name.
  @param expression
  @return flag true/false