如何为文本制作正则表达式？

Question

我有一个用户模型，我有简要介绍＆＃34;介绍＆＃34;我的用户模型中用户的类型是字符串，如下所示。

  VALID_INTRO_REGEX = /\A[a-zA-Z\.\,]+(?: [a-zA-Z\.\,]+)*\z/
  validates :intro, presence: true, length: { maximum: 255 },
                    format: { with: VALID_INTRO_REGEX, :message => "must contain only letters" }

如何制作满足以下有效和无效语句的正则表达式？

Valid = "Hey everyone! My name is xxxx. I am from XXX. I do this, I do that."   
Invalid = "<img src= "    
Invalid = "">< img src=x onerror=alert(0);>"