minify-html/notes/Parsing.md

# Parsing

minify-html does not have any error states and will always output a value. This means that all possible ambiguous or malformed states need to be handled. This document describes these.

minify-html tries to match what the specs dictate and modern browsers do. However, there may be occasional differences for malformed syntax, as the browser and spec rules are very complex when handling invalid HTML.

To see some complex inputs, check out the [various fuzzing inputs](../fuzz/in).

## Limitations

- Input must be valid UTF-8 without BOM.
- All HTML is interpreted as HTML5.
- [Escaped and double-escaped](./Script%20data.md) script content are not supported.

## EOF

If the input ends while in the middle of a tag or attribute value, that tag/attribute is closed, as well as all ancestor tags.

## Tags

|Rule|Example source|Example interpretation|
|---|---|---|
|A tag name is one or more alphanumeric, `:`, or `-` characters|`<x:a:b:--d09>`|`<x:a:b:--d09>`|
|`script`, `style`, `textarea`, and `title` tags do not close until the case-insensitive sequence `</` followed by the tag name.|`<teXTaRea></textare></TEXTArea>`|`<textarea></textare></textarea>`|
|Attribute-like syntax in closing tags are parsed like attributes but ignored.|`<div></div x=">">5`|`<div></div>`|
|If the character following `</` is not a valid tag name character, all code until the next `>` is dropped. It is not considered a closing tag, even as an invalid one.|`<div></   div x=">">5`|`<div>">5`|
|If a closing tag represents a void element, the closing tag is dropped.|`<div><br>ax</br><img></img>i</div>`|`<div><br>ax<img>i</div>`|
|If a closing tag does not match the opening tag, and the closing tag cannot be omitted as per the spec, the closing tag is ignored. NOTE: Most browsers have far more complex logic.|`<div><span></div></span>5`|`<div><span><span>5`|
|If an opening tag ends with `/>` instead of `>`, and it's an HTML tag, the `/` is ignored. If it's an SVG tag, it's self-closing.|`<div/>5<div></div>`|`<div>5<div></div>`|
|A slash as the last character of an unquoted attribute value immediately preceding a `>` is not interpreted as part of the self-closing syntax `/>`, even for self-closable SVG elements.|`<circle r=1/>`|`<circle r="1/">`|
|Any opening `html`, `head`, or `body` tags after the first are ignored.|`<html><head><meta><body><div><head><span><body>`|`<html><head><meta><body><div><span>`|
|Any closing `html` or `body` tags, or `head` after the first, are ignored.|`<html><head><meta><body><div></body><span></body><input></html><a>`|`<html><head><meta><body><div><span><input><a>`|
|If a `<` in content is not followed by an alphanumeric, `:`, or `=` character, it is interpreted as a literal `<`, as per the [spec](https://html.spec.whatwg.org/multipage/syntax.html#syntax-tag-name).|`<div>< /div>< span>`|`<div>< /div>< span>`|

## Attributes

|Rule|Example source|Example interpretation|
|---|---|---|
|Whitespace can exist between an `=` and the attribute name and value.|`a   =  =b=`|`a="=b="`|
|An unquoted attribute value continues until the next `>` or whitespace character.|`a = b"cdef/>`|`a='b"cdef/'>`|
|Whitespace and slashes separate attributes, but not around `=`.|`a  = b /c/d==/e=/f`|`a="b" c="" d="=" e="/f"`|
|An attribute name starts with any character other than a whitespace, `/`, or `>` (`=` is allowed) and continues until the next `=`, `/`, `>`, or whitespace character.|`== "a":  {}#$'=/>`|`=="" "a":="" {}#$'="" />`|
|If multiple attributes exist with the same case-insensitive name, only the last is kept.|`a=b a=c b=c a=d`|`b=c a=d`|
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00			`# Parsing`

Implement core minifier 2021-08-06 02:17:45 -04:00			`minify-html does not have any error states and will always output a value. This means that all possible ambiguous or malformed states need to be handled. This document describes these.`
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00
Minor clarification 2021-08-07 11:52:25 -04:00			`minify-html tries to match what the specs dictate and modern browsers do. However, there may be occasional differences for malformed syntax, as the browser and spec rules are very complex when handling invalid HTML.`
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00
			`To see some complex inputs, check out the [various fuzzing inputs](../fuzz/in).`

Update README 2021-08-07 11:10:40 -04:00			`## Limitations`

Minor clarifications 2021-08-07 11:12:41 -04:00			`- Input must be valid UTF-8 without BOM.`
Update README 2021-08-07 11:10:40 -04:00			`- All HTML is interpreted as HTML5.`
			`- [Escaped and double-escaped](./Script%20data.md) script content are not supported.`

Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00			`## EOF`

			`If the input ends while in the middle of a tag or attribute value, that tag/attribute is closed, as well as all ancestor tags.`

			`## Tags`

			`\|Rule\|Example source\|Example interpretation\|`
			`\|---\|---\|---\|`
Implement attr minification; various parser and minifier fixes 2021-08-06 07:56:54 -04:00			\|A tag name is one or more alphanumeric, `:`, or `-` characters\|`<x:a:b:--d09>`\|`<x:a:b:--d09>`\|
Ignore html/head/body duplicate tags while parsing, omit them when minifying; parse <title> correctly 2021-08-07 01:59:41 -04:00			\|`script`, `style`, `textarea`, and `title` tags do not close until the case-insensitive sequence `</` followed by the tag name.\|`<teXTaRea></textare></TEXTArea>`\|`<textarea></textare></textarea>`\|
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00			\|Attribute-like syntax in closing tags are parsed like attributes but ignored.\|`<div></div x=">">5`\|`<div></div>`\|
Implement core minifier 2021-08-06 02:17:45 -04:00			\|If the character following `</` is not a valid tag name character, all code until the next `>` is dropped. It is not considered a closing tag, even as an invalid one.\|`<div></ div x=">">5`\|`<div>">5`\|
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00			\|If a closing tag represents a void element, the closing tag is dropped.\|`<div><br>ax</br><img></img>i</div>`\|`<div><br>ax<img>i</div>`\|
Drop mismatched closing tags instead of reinterpreting as opening tags 2022-06-22 06:13:36 -04:00			\|If a closing tag does not match the opening tag, and the closing tag cannot be omitted as per the spec, the closing tag is ignored. NOTE: Most browsers have far more complex logic.\|`<div><span></div></span>5`\|`<div><span><span>5`\|
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00			\|If an opening tag ends with `/>` instead of `>`, and it's an HTML tag, the `/` is ignored. If it's an SVG tag, it's self-closing.\|`<div/>5<div></div>`\|`<div>5<div></div>`\|
			\|A slash as the last character of an unquoted attribute value immediately preceding a `>` is not interpreted as part of the self-closing syntax `/>`, even for self-closable SVG elements.\|`<circle r=1/>`\|`<circle r="1/">`\|
			\|Any opening `html`, `head`, or `body` tags after the first are ignored.\|`<html><head><meta><body><div><head><span><body>`\|`<html><head><meta><body><div><span>`\|
Fix tag omission minification; implement entity reencoding minification 2021-08-06 08:53:33 -04:00			\|Any closing `html` or `body` tags, or `head` after the first, are ignored.\|`<html><head><meta><body><div></body><span></body><input></html><a>`\|`<html><head><meta><body><div><span><input><a>`\|
Minor phrasing changes 2022-03-21 21:44:14 -04:00			\|If a `<` in content is not followed by an alphanumeric, `:`, or `=` character, it is interpreted as a literal `<`, as per the [spec](https://html.spec.whatwg.org/multipage/syntax.html#syntax-tag-name).\|`<div>< /div>< span>`\|`<div>< /div>< span>`\|
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00
			`## Attributes`

			`\|Rule\|Example source\|Example interpretation\|`
			`\|---\|---\|---\|`
			\|Whitespace can exist between an `=` and the attribute name and value.\|`a = =b=`\|`a="=b="`\|
Implement attr minification; various parser and minifier fixes 2021-08-06 07:56:54 -04:00			\|An unquoted attribute value continues until the next `>` or whitespace character.\|`a = b"cdef/>`\|`a='b"cdef/'>`\|
Implement parser; remove legacy code 2021-08-05 22:07:27 -04:00			\|Whitespace and slashes separate attributes, but not around `=`.\|`a = b /c/d==/e=/f`\|`a="b" c="" d="=" e="/f"`\|
Minor phrasing changes 2022-03-21 21:44:14 -04:00			\|An attribute name starts with any character other than a whitespace, `/`, or `>` (`=` is allowed) and continues until the next `=`, `/`, `>`, or whitespace character.\|`== "a": {}#$'=/>`\|`=="" "a":="" {}#$'="" />`\|
			\|If multiple attributes exist with the same case-insensitive name, only the last is kept.\|`a=b a=c b=c a=d`\|`b=c a=d`\|