code: public static Selector expressionSelector(String expr, EvaluationContext evalCtx) {
          return new ExpressionSelector(SPEL_PARSER.parseExpression(expr), evalCtx);
      }
docs: Helper method for creating an {@code ExpressionSelector}.
  
  @param expr
  The expression to parse.
  @param evalCtx
  The {@link org.springframework.expression.EvaluationContext} to use.
  
  @return A new {@link reactor.bus.selector.Selector}