Boolean properties that map to element's attributes

[g105b]

There is inconsistent behaviour when working with boolean properties that map directly to an element's attribute. For example: $element->disabled = true should add the attribute disabled to the element, without a value. Subsequently, $element->disabled = false should remove the attribute. This is the same for selected, checked, etc.

• Step 1: List out all the boolean properties from a comprehensive list on official documentation such as W3C or MDN.
• Step 2: Validate that there is incorrect behaviour by isolating this issue in a unit test.
• Step 3: Implement consistent behaviour with the above.

[g105b]

Collating from https://www.w3.org/TR/html52/fullindex.html#ref-for-boolean-attribute%E2%91%A2%E2%91%A1 :

(this must be documented in full within this repo at some point)

• allowfullscreen
• allowpaymentrequest
• async
• autofocus
• autoplay
• checked
• controls
• default
• defer
• disabled
• formnovalidate
• hidden
• ismap
• loop
• multiple
• muted
• novalidate
• open
• readonly
• required
• reversed
• selected
• typemustmatch