SELECTORS

-	I studied this selector before
+	I need to do research for this selector

https://www.w3.org/TR/selectors-4/
https://drafts.csswg.org/selectors/

Selector basics

-	Element selector
-	Class selector
-	ID selector
-	Descendant selector
-	,
-	*
- 	+
-	>
-	~
-	[attr] + permutations


-	Explanation of pseudo-classes and pseudo-elements

User action

-	:active
-	:focus :focus-visible :focus-within, 
+	:-moz-user-focus -> check if this helps with :valid/:invalid
-	:hover
-	:target
+	:target-within

Functional

-	:not()
+	:is()
+	:where()
+	:has()

Input (forms)

-	:checked
-	:default
-	:disabled
-	:enabled
-	:in-range and :out-of-range
-	:invalid and :valid
-	:optional
-	:read-only and :read-write
-	:required
-	:indeterminate
+	:autofill
+	:placeholder-shown
+	::placeholder
+	:blank
+	:user-invalid and :user-valid

Previous research:
https://www.quirksmode.org/blog/archives/2017/12/native_form_val.html
https://www.quirksmode.org/blog/archives/2017/12/native_form_val_1.html
https://www.quirksmode.org/blog/archives/2017/12/native_form_val_2.html

Tree structure

-	:first/last-of-type
-	:first-child and :last-child
-	:nth-child + last
-	:nth-of-type + last
	+	nth-child(4 of S)
-	:only-child
-	:only-of-type
-	:empty
-	:root -> overused, why not simply html?
-	::first-letter and ::first-line
		::prefix and ::postfix
+	:part() for options in select

	Tree-Abiding Pseudo-elements

	-	::before and ::after
	+	::marker
	(placeholder, but better with forms)
	+	::file-selector-button


Nesting

Not a selector per se, but needs to be treated here.

Miscellaneous
	
	highlight

	-	::selection
	+	::target-text
	
	tables

	+	|| -> column.selected || td -> only for table columns?
	+	nth-col() and nth-last-col()

+	:defined
-	:link :visited :any-link :local-link
+	:scope
+	:fullscreen -> mobile browsers are always fullscreen
+	:modal
+	:picture-in-picture
+	:dir()
+	:lang()
+	:playing and :paused
+	::backdrop