Changes

Haml 6 has some [breaking changes](https://github.com/haml/haml/blob/main/CHANGELOG.md#600) regarding [boolean attributes](https://github.com/haml/haml/issues/1091).
 > Only the following attributes and `aria`/`data` attributes are considered boolean attributes: `allowfullscreen`, `async`, `autobuffer`, `autofocus`, `autoplay`, `checked`, `controls`, `default`,  `defer`, `disabled`, `download`, `formnovalidate`, `hidden`, `inert`, `ismap`, `itemscope`, `loop`, `multiple`, `muted`, `novalidate`, `open`, `pubdate`, `readonly`, `required`, `reversed`, `scoped`,
       `seamless`, `selected`, `sortable`, `truespeed`, `typemustmatch`
This requires you to change custom attributes in case you want them to be an attribute without a value e.g. `a(up-test)` has to be changed to `a(up-test='')` in HAML 6.
## Examples
| Haml (no breaking changes)                       | Version 5 | Version 6 |
|----------------------------|-----------|-----------|
| %button(disabled)          | `<button disabled=""></button>`          | `<button disabled=""></button>`          |
| %button(disabled=true)     | `<button disabled=""></button>`          | `<button disabled=""></button>`          |
| %button(disabled=false)    | `<button></button>`          | `<button></button>`          |
| %button(disabled='true')   | `<button disabled="true"></button>`          | `<button disabled="true"></button>`          |
| %button(disabled='false')  | `<button disabled="false"></button>`          | `<button disabled="false"></button>`          |
| %button(disabled='')       | `<button disabled=""></button>`          | `<button disabled=""></button>`          |
| Haml (no breaking changes)                      | Version 5 | Version 6 |
|----------------------------|-----------|-----------|
| %button(data-test)         | `<button data-test=""></button>`          | `<button data-test=""></button>`          |
| %button(data-test=true)    | `<button data-test=""></button>`          | `<button data-test=""></button>`          |
| %button(data-test=false)   | `<button></button>`          | `<button></button>`          |
| %button(data-test='true')  | `<button data-test="true"></button>`          | `<button data-test="true"></button>`          |
| %button(data-test='false') | `<button data-test="false"></button>`          | `<button data-test="false"></button>`          |
| %button(data-test='')      | `<button data-test=""></button>`          | `<button data-test=""></button>`          |
| Haml (with breaking changes)                       | Version 5 | Version 6 |
|----------------------------|-----------|-----------|
| %button(up-test)           | `<button up-test=""></button>`          | `<button up-test="true"></button>`          |
| %button(up-test=true)      | `<button up-test=""></button>`          | `<button up-test="true"></button>`          |
| %button(up-test=false)     | `<button></button>`          | `<button up-test="false"></button>`          |
| %button(up-test='true')    | `<button up-test="true"></button>`          | `<button up-test="true"></button>`          |
| %button(up-test='')    | `<button up-test=""></button>`          | `<button up-test=""></button>`          |
## Monkey Patch
In case you want to reconfigure the attributes that a recognized as boolean attributes you can use a monkey patch in an initializer. For example, the following would consider all attributes prefixed with `app-` to be boolean attributes:
```ruby
### Haml 6.3 and newer
Haml.class_eval do
  remove_const(:BOOLEAN_ATTRIBUTES).tap do |boolean_attributes|
    const_set(:BOOLEAN_ATTRIBUTES, [*boolean_attributes, /^app-/].freeze)
  end
end
### Haml 6.0 - 6.2.x
Haml::AttributeBuilder.class_eval do
  remove_const(:BOOLEAN_ATTRIBUTES).tap do |boolean_attributes|
    const_set(:BOOLEAN_ATTRIBUTES, [*boolean_attributes, /^app-/].freeze)
  end
end
```
Note: You might want to consider using `data` attributes for all your custom attributes e.g. `scrollable` => `data-scrollable`. It might still be legit to allow framework prefixes in case they do not support `data` attributes e.g. `ng-` (Angular) or `up-` (Unpoly).
-But be very selective about patching `up-` attributes so you can still use expressions like `[up-follow=false]` or `[up-history=false]`.
+
+## Boolean [Unpoly](https://unpoly.com) attributes
+
+Be very selective about patching `up-` attributes so you can still use expressions like `[up-follow=false]` or `[up-history=false]`.
+
+Starting with [Unpoly 3.8](https://github.com/unpoly/unpoly/discussions/646), most Unpoly attributes can now be enabled with a value `"true"` and be disabled with a value `"false"`. This pairs well with the default (unpatched) Haml 6 behavior.
+
A different approach is to create attributes from a ruby hash:
+
```haml
%tr{ { 'up-expand': ('' if superuser?) }.compact }
```
+
This will provide you with `<tr up-expand="">` for a superuser and `<tr>` otherwise.