HTML: Self-Closing Tags

# HTML: Self-Closing Tags

A foreign element's start tag can be *marked as* self-closing; for
example:

```HTML

<svg>
    
    <circle cx="30" cy="10" r="20" />
</svg>
```

A void element can be *written like* a self-closing tag; for example:

```HTML

<br>
<hr />
```

# References

[8.1.2.1. Start tags](https://www.w3.org/TR/2021/SPSD-html52-20210128/syntax.html#start-tags):

> Then, if the element is one of the void elements, or if the element is
> a foreign element, then there may be a single U+002F SOLIDUS character
> (`/`). This character has no effect on void elements, but on foreign
> elements it marks the start tag as self-closing.

[Foreign elements](https://www.w3.org/TR/2021/SPSD-html52-20210128/syntax.html#foreign-elements):

> Elements from the MathML namespace and the SVG namespace.

[Void elements](https://www.w3.org/TR/2021/SPSD-html52-20210128/syntax.html#void-elements):

> `area`, `base`, `br`, `col`, `embed`, `hr`, `img`, `input`, `link`,
> `meta`, `param`, `source`, `track`, `wbr`

[8.1.2. Elements](https://www.w3.org/TR/2021/SPSD-html52-20210128/syntax.html#writing-html-documents-elements):

> Void elements only have a start tag; end tags must not be specified
> for void elements.

> Foreign elements must either have a start tag and an end tag, or a
> start tag that is marked as self-closing, in which case they must not
> have an end tag.

> Void elements can’t have any contents (since there’s no end tag, no
> content can be put between the start tag and the end tag).

> Foreign elements whose start tag is marked as self-closing can’t have
> any contents (since, again, as there’s no end tag, no content can be
> put between the start tag and the end tag). Foreign elements whose
> start tag is not marked as self-closing can have text, character
> references, CDATA sections, other elements, and comments, but the text
> must not contain the character U+003C LESS-THAN SIGN (`<`) or an
> ambiguous ampersand.

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