See [corresponding blog post](http://perfectionkills.com/experimenting-with-html-minifier/) for all the gory details of [how it works](http://perfectionkills.com/experimenting-with-html-minifier/#how_it_works), [description of each option](http://perfectionkills.com/experimenting-with-html-minifier/#options), [testing results](http://perfectionkills.com/experimenting-with-html-minifier/#field_testing) and [conclusions](http://perfectionkills.com/experimenting-with-html-minifier/#cost_and_benefits).
Also see corresponding [Ruby wrapper](https://github.com/stereobooster/html_minifier), and for Node.js, [Grunt plugin](https://github.com/gruntjs/grunt-contrib-htmlmin), [Gulp module](https://github.com/jonschlinkert/gulp-htmlmin), [Koa middleware wrapper](https://github.com/koajs/html-minifier) and [Express middleware wrapper](https://github.com/melonmanchan/express-minify-html).
For lint-like capabilities take a look at [HTMLLint](https://github.com/kangax/html-lint).
## Minification comparison
How does HTMLMinifier compare to other solutions — [HTML Minifier from Will Peavy](http://www.willpeavy.com/minifier/) (1st result in [Google search for "html minifier"](https://www.google.com/#q=html+minifier)) as well as [htmlcompressor.com](http://htmlcompressor.com) and [minimize](https://github.com/Swaagie/minimize)?
| `collapseInlineTagWhitespace` | Don't leave any spaces between `display:inline;` elements when collapsing. Must be used in conjunction with `collapseWhitespace=true` | `false` |
| `collapseWhitespace` | [Collapse white space that contributes to text nodes in a document tree](http://perfectionkills.com/experimenting-with-html-minifier/#collapse_whitespace) | `false` |
| `conservativeCollapse` | Always collapse to 1 space (never remove it entirely). Must be used in conjunction with `collapseWhitespace=true` | `false` |
| `customAttrAssign` | Arrays of regex'es that allow to support custom attribute assign expressions (e.g. `'<div flex?="{{mode != cover}}"></div>'`) | `[ ]` |
| `customAttrCollapse` | Regex that specifies custom attribute to strip newlines from (e.g. `/ng-class/`) | |
| `customAttrSurround` | Arrays of regex'es that allow to support custom attribute surround expressions (e.g. `<input {{#if value}}checked="checked"{{/if}}>`) | `[ ]` |
| `customEventAttributes` | Arrays of regex'es that allow to support custom event attributes for `minifyJS` (e.g. `ng-click`) | `[ /^on[a-z]{3,}$/ ]` |
| `decodeEntities` | Use direct Unicode characters whenever possible | `false` |
| `html5` | Parse input according to HTML5 specifications | `true` |
| `ignoreCustomComments` | Array of regex'es that allow to ignore certain comments, when matched | `[ /^!/ ]` |
| `ignoreCustomFragments` | Array of regex'es that allow to ignore certain fragments, when matched (e.g. `<?php ... ?>`, `{{ ... }}`, etc.) | `[ /<%[\s\S]*?%>/, /<\?[\s\S]*?\?>/ ]` |
| `includeAutoGeneratedTags` | Insert tags generated by HTML parser | `true` |
| `keepClosingSlash` | Keep the trailing slash on singleton elements | `false` |
| `maxLineLength` | Specify a maximum line length. Compressed output will be split by newlines at valid HTML split-points |
| `minifyJS` | Minify JavaScript in script elements and event attributes (uses [UglifyJS](https://github.com/mishoo/UglifyJS2)) | `false` (could be `true`, `Object`, `Function(text, inline)`) |
| `minifyURLs` | Minify URLs in various attributes (uses [relateurl](https://github.com/stevenvachon/relateurl)) | `false` (could be `String`, `Object`, `Function(text)`) |
| `preserveLineBreaks` | Always collapse to 1 line break (never remove it entirely) when whitespace between tags include a line break. Must be used in conjunction with `collapseWhitespace=true` | `false` |
| `preventAttributesEscaping` | Prevents the escaping of the values of attributes | `false` |
| `processConditionalComments` | Process contents of conditional comments through minifier | `false` |
| `processScripts` | Array of strings corresponding to types of script elements to process through minifier (e.g. `text/ng-template`, `text/x-handlebars-template`, etc.) | `[ ]` |
| `quoteCharacter` | Type of quote to use for attribute values (' or ") | |
| `removeAttributeQuotes` | [Remove quotes around attributes when possible](http://perfectionkills.com/experimenting-with-html-minifier/#remove_attribute_quotes) | `false` |
| `removeComments` | [Strip HTML comments](http://perfectionkills.com/experimenting-with-html-minifier/#remove_comments) | `false` |
| `removeEmptyAttributes` | [Remove all attributes with whitespace-only values](http://perfectionkills.com/experimenting-with-html-minifier/#remove_empty_or_blank_attributes) | `false` (could be `true`, `Function(attrName, tag)`) |
| `removeEmptyElements` | [Remove all elements with empty contents](http://perfectionkills.com/experimenting-with-html-minifier/#remove_empty_elements) | `false` |
| `trimCustomFragments` | Trim white space around `ignoreCustomFragments`. | `false` |
| `useShortDoctype` | [Replaces the `doctype` with the short (HTML5) doctype](http://perfectionkills.com/experimenting-with-html-minifier/#use_short_doctype) | `false` |
### Sorting attributes / style classes
Minifier options like `sortAttributes` and `sortClassName` won't impact the plain-text size of the output. However, they form long repetitive chains of characters that should improve compression ratio of gzip used in HTTP compression.
## Special cases
### Ignoring chunks of markup
If you have chunks of markup you would like preserved, you can wrap them `<!-- htmlmin:ignore -->`.
### Preserving SVG tags
SVG tags are automatically recognized, and when they are minified, both case-sensitivity and closing-slashes are preserved, regardless of the minification settings used for the rest of the file.
### Working with invalid markup
HTMLMinifier **can't work with invalid or partial chunks of markup**. This is because it parses markup into a tree structure, then modifies it (removing anything that was specified for removal, ignoring anything that was specified to be ignored, etc.), then it creates a markup out of that tree and returns it.
Input markup (e.g. `<p id="">foo`)
↓
Internal representation of markup in a form of tree (e.g. `{ tag: "p", attr: "id", children: ["foo"] }`)
↓
Transformation of internal representation (e.g. removal of `id` attribute)
↓
Output of resulting markup (e.g. `<p>foo</p>`)
HTMLMinifier can't know that original markup was only half of the tree; it does its best to try to parse it as a full tree and it loses information about tree being malformed or partial in the beginning. As a result, it can't create a partial/malformed tree at the time of the output.
