HTML

4.14 Matching HTML elements using selectors

4.14.1 Case-sensitivity

The Selectors specification leaves the case-sensitivity of IDs, classes, element names, attribute names, and attribute values to be defined by the host language. [SELECTORS]

The unique identifier of HTML elements in documents that are in quirks mode must be treated as ASCII case-insensitive for the purposes of selector matching.

Classes from the class attribute of HTML elements in documents that are in quirks mode must be treated as ASCII case-insensitive for the purposes of selector matching.

Attribute and element names of HTML elements in HTML documents must be treated as ASCII case-insensitive for the purposes of selector matching.

Everything else (attribute values on HTML elements, IDs and classes in no-quirks mode and limited-quirks mode, and element names, attribute names, and attribute values in XML documents) must be treated as case-sensitive for the purposes of selector matching.

4.14.2 Pseudo-classes

There are a number of dynamic selectors that can be used with HTML. This section defines when these selectors match HTML elements. [SELECTORS] [CSSUI]

:link

:visited

All a elements that have an href attribute, all area elements that have an href attribute, and all link elements that have an href attribute, must match one of :link and :visited.

Other specifications might apply more specific rules regarding how these elements are to match these pseudo-elements, to mitigate some privacy concerns that apply with straightforward implementations of this requirement.

:active

The :active pseudo-class is defined to match an element while an element is being activated by the user. For the purposes of defining the :active pseudo-class only, an HTML user agent must consider an element as being activated if it is:

• An element falling into one of the following categories between the time the user begins to indicate an intent to trigger the element's activation behavior and either the time the user stops indicating an intent to trigger the element's activation behavior, or the time the element's activation behavior has finished running, which ever comes first:

  • a elements that have an href attribute
  • area elements that have an href attribute
  • link elements that have an href attribute
  • button elements that are not disabled
  • input elements whose type attribute is in the Submit Button, Image Button, Reset Button, or Button state
  • command elements that do not have a disabled attribute
  • elements that have their tabindex focus flag set

  For example, if the user is using a keyboard to push a button element by pressing the space bar, the element would match this pseudo-class in between the time that the element received the keydown event and the time the element received the keyup event.

• An element that the user indicates using a pointing device while that pointing device is in the "down" state (e.g. for a mouse, between the time the mouse button is pressed and the time it is depressed).

• An element that has a descendant that is currently matching the :active pseudo-class.

:enabled

The :enabled pseudo-class must match any element falling into one of the following categories:

• a elements that have an href attribute
• area elements that have an href attribute
• link elements that have an href attribute
• button elements that are not disabled
• input elements whose type attribute are not in the Hidden state and that are not disabled
• select elements that are not disabled
• textarea elements that are not disabled
• optgroup elements that do not have a disabled attribute
• option elements that are not disabled
• command elements that do not have a disabled attribute
• li elements that are children of menu elements, and that have a child element that defines a command, if the first such element's Disabled State facet is false (not disabled)
• fieldset elements that do not have a disabled attribute

:disabled

The :disabled pseudo-class must match any element falling into one of the following categories:

• button elements that are disabled
• input elements whose type attribute are not in the Hidden state and that are disabled
• select elements that are disabled
• textarea elements that are disabled
• optgroup elements that have a disabled attribute
• option elements that are disabled
• command elements that have a disabled attribute
• li elements that are children of menu elements, and that have a child element that defines a command, if the first such element's Disabled State facet is true (disabled)
• fieldset elements that have a disabled attribute

:checked

The :checked pseudo-class must match any element falling into one of the following categories:

• input elements whose type attribute is in the Checkbox state and whose checkedness state is true
• input elements whose type attribute is in the Radio Button state and whose checkedness state is true
• option elements whose selectedness is true
• command elements whose type attribute is in the Checkbox state and that have a checked attribute
• command elements whose type attribute is in the Radio state and that have a checked attribute

:indeterminate

The :indeterminate pseudo-class must match any element falling into one of the following categories:

• input elements whose type attribute is in the Checkbox state and whose indeterminate IDL attribute is set to true
• progress elements with no value content attribute

:default

The :default pseudo-class must match any element falling into one of the following categories:

• button elements that are their form's default button
• input elements whose type attribute is in the Submit Button or Image Button state, and that are their form's default button
• input elements to which the checked attribute applies and that have a checked attribute
• option elements that have a selected attribute

:valid

The :valid pseudo-class must match any element falling into one of the following categories:

• elements that are candidates for constraint validation and that satisfy their constraints
• form elements that are not the form owner of any elements that themselves are candidates for constraint validation but do not satisfy their constraints

:invalid

The :invalid pseudo-class must match any element falling into one of the following categories:

• elements that are candidates for constraint validation but that do not satisfy their constraints
• form elements that are the form owner of one or more elements that themselves are candidates for constraint validation but do not satisfy their constraints

:in-range

The :in-range pseudo-class must match all elements that are candidates for constraint validation, have range limitations, and that are neither suffering from an underflow nor suffering from an overflow.

:out-of-range

The :out-of-range pseudo-class must match all elements that are candidates for constraint validation, have range limitations, and that are either suffering from an underflow or suffering from an overflow.

:required

The :required pseudo-class must match any element falling into one of the following categories:

• input elements that are required
• select elements that have a required attribute
• textarea elements that have a required attribute

:optional

The :optional pseudo-class must match any element falling into one of the following categories:

• input elements to which the required attribute applies that are not required
• select elements that do not have a required attribute
• textarea elements that do not have a required attribute

:read-only

:read-write

The :read-write pseudo-class must match any element falling into one of the following categories:

• input elements to which the readonly attribute applies, but that are not immutable (i.e. that do not have the readonly attribute specified and that are not disabled)
• textarea elements that do not have a readonly attribute, and that are not disabled
• elements that are editing hosts or editable and are neither input elements nor textarea elements

The :read-only pseudo-class must match all other HTML elements.

:dir(ltr)

The :dir(ltr) pseudo-class must match all elements whose directionality is 'ltr'.

:dir(rtl)

The :dir(rtl) pseudo-class must match all elements whose directionality is 'rtl'.

Another section of this specification defines the target element used with the :target pseudo-class.

This specification does not define when an element matches the :hover, :focus, or :lang() dynamic pseudo-classes, as those are all defined in sufficient detail in a language-agnostic fashion in the Selectors specification. [SELECTORS]