if type undefined

When you type "undefined" into an HTML document, you will get no result. To understand why this is, you need to understand a bit about how the web browser interprets HTML code. HTML documents are composed of HTML elements, which are sets of tags that tell the browser how to render the page. HTML tags usually contain content, like text or images. However, some tags do not contain content, but only provide attributes to the HTML elements that they enclose. An example of such a tag is the tag. It does not contain content, but instead provides an attribute to the element that it encloses. This attribute is "undefined". When the browser encounters the  tag, it reads the "undefined" attribute and sets the element to "undefined". This means that the element will not be rendered to the page. It is "invisible" to the browser. The same concept applies to other HTML elements as well. Any attribute that is set to "undefined" will cause that element to not be rendered.

<div style="undefined">
  Content
</div>

In the above example, the  element will not be rendered because its "style" attribute was set to "undefined". This means that any content within the  element will not be visible on the page. However, there are many cases where setting the "undefined" attribute is useful. For example, if you want to create a "hint" style element, which is only visible when the user hovers over it, you can set the element's "display" attribute to "undefined". This will cause the element to only become visible when the user hovers over it.

<div style="display: undefined;">
  Hint content
</div>

In this example, the element will not be visible until the user hovers over it. This can be useful for creating interactive elements on a page. In conclusion, when you type "undefined" into an HTML document, it will not be rendered because the browser interprets it as an attribute that is set to "undefined". However, this attribute can be useful for creating interactive elements on a page, like hints or elements that only become visible when the user hovers over them.