为什么 <content> 标签必须以开始标签和结束标签定义？

Question

I used these two syntaxes in Firefox/Chrome to define a WebComponent.

Open tag

<content></content>

Closed tag

<content/>

and both work as expected.

What are the (technical) reasons for defining <content> in the first way?

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MDN Content element indicates that a starting and ending tag is mandatory , but doesn't specify why.

Answer 1

You actually must use the <content></content> form. In a normal HTML (non-XML) document (which is what you want to be making here), with the standard way that HTML parsing works in all browser engines, the <content/> tag is not a content end tag—instead it's just a content start tag with an extra / inside it that just gets ignored by HTML parsers.

In your case, that means when an HTML parser doesn't see any </content> end tag for that content -start-tag-with-extra- / -at-the end, the parser never actually closes that content element , so that *all nodes that follow that content element become child content of it.

To see what I mean, look at the DOM view of what the <content/> looks like to an HTML parser .

MDN Content element indicates that the empty tag form is mandatory, but doesn't specify why.

I'm not sure what you mean by “empty tag form”. That MDN page says:

Tag omission : None, both the starting and ending tag are mandatory.

That means the content element must have an end tag.