ElementInternals

Form-associated custom elements form-associated-custom-elements

Baseline: Widely available on the web, in every major browser since Mar 2023, and long enough to count on (since Sep 2025).

niso: Partial 2.4%. 3 of 123 subtests pass, by system: Linux 2.4%, macOS 2.4%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · ElementInternals, HTMLElement

ElementInternals is an interface in idl/html.webidl, exposed in Window. It includes ARIAMixin. What it does is on MDN; this page says what niso has of it.

Status

The web features its members belong to, each with its Baseline status on the web and how much of the feature’s WPT suite passes in niso (see Web platform support).

Feature	On the web	In niso	Members
ARIA attribute reflection	Widely available	Full 41 of 41 subtests pass	43
Form-associated custom elements	Widely available	Partial 2.4% 3 of 123 subtests pass	2

Members

form

attribute

readonly attribute HTMLFormElement? form;

int32_t niso_element_internals_get_form(niso_dom* dom, niso_handle self, niso_handle* out);

role

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? role;

int32_t niso_aria_mixin_get_role(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_role(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaAtomic

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaAtomic;

int32_t niso_aria_mixin_get_aria_atomic(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_atomic(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaAutoComplete

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaAutoComplete;

int32_t niso_aria_mixin_get_aria_auto_complete(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_auto_complete(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaBrailleLabel

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaBrailleLabel;

int32_t niso_aria_mixin_get_aria_braille_label(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_braille_label(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaBrailleRoleDescription

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaBrailleRoleDescription;

int32_t niso_aria_mixin_get_aria_braille_role_description(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_braille_role_description(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaBusy

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaBusy;

int32_t niso_aria_mixin_get_aria_busy(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_busy(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaChecked

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaChecked;

int32_t niso_aria_mixin_get_aria_checked(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_checked(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaColCount

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaColCount;

int32_t niso_aria_mixin_get_aria_col_count(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_col_count(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaColIndex

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaColIndex;

int32_t niso_aria_mixin_get_aria_col_index(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_col_index(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaColIndexText

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaColIndexText;

int32_t niso_aria_mixin_get_aria_col_index_text(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_col_index_text(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaColSpan

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaColSpan;

int32_t niso_aria_mixin_get_aria_col_span(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_col_span(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaCurrent

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaCurrent;

int32_t niso_aria_mixin_get_aria_current(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_current(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaDescription

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaDescription;

int32_t niso_aria_mixin_get_aria_description(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_description(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaDisabled

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaDisabled;

int32_t niso_aria_mixin_get_aria_disabled(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_disabled(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaExpanded

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaExpanded;

int32_t niso_aria_mixin_get_aria_expanded(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_expanded(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaHasPopup

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaHasPopup;

int32_t niso_aria_mixin_get_aria_has_popup(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_has_popup(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaHidden

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaHidden;

int32_t niso_aria_mixin_get_aria_hidden(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_hidden(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaInvalid

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaInvalid;

int32_t niso_aria_mixin_get_aria_invalid(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_invalid(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaKeyShortcuts

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaKeyShortcuts;

int32_t niso_aria_mixin_get_aria_key_shortcuts(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_key_shortcuts(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaLabel

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaLabel;

int32_t niso_aria_mixin_get_aria_label(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_label(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaLevel

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaLevel;

int32_t niso_aria_mixin_get_aria_level(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_level(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaLive

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaLive;

int32_t niso_aria_mixin_get_aria_live(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_live(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaModal

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaModal;

int32_t niso_aria_mixin_get_aria_modal(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_modal(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaMultiLine

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaMultiLine;

int32_t niso_aria_mixin_get_aria_multi_line(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_multi_line(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaMultiSelectable

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaMultiSelectable;

int32_t niso_aria_mixin_get_aria_multi_selectable(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_multi_selectable(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaOrientation

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaOrientation;

int32_t niso_aria_mixin_get_aria_orientation(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_orientation(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaPlaceholder

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaPlaceholder;

int32_t niso_aria_mixin_get_aria_placeholder(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_placeholder(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaPosInSet

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaPosInSet;

int32_t niso_aria_mixin_get_aria_pos_in_set(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_pos_in_set(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaPressed

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaPressed;

int32_t niso_aria_mixin_get_aria_pressed(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_pressed(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaReadOnly

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaReadOnly;

int32_t niso_aria_mixin_get_aria_read_only(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_read_only(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRelevant

attribute from ARIAMixin

attribute DOMString? ariaRelevant;

int32_t niso_aria_mixin_get_aria_relevant(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_relevant(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRequired

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaRequired;

int32_t niso_aria_mixin_get_aria_required(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_required(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRoleDescription

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaRoleDescription;

int32_t niso_aria_mixin_get_aria_role_description(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_role_description(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRowCount

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaRowCount;

int32_t niso_aria_mixin_get_aria_row_count(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_row_count(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRowIndex

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaRowIndex;

int32_t niso_aria_mixin_get_aria_row_index(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_row_index(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRowIndexText

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaRowIndexText;

int32_t niso_aria_mixin_get_aria_row_index_text(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_row_index_text(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaRowSpan

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaRowSpan;

int32_t niso_aria_mixin_get_aria_row_span(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_row_span(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaSelected

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaSelected;

int32_t niso_aria_mixin_get_aria_selected(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_selected(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaSetSize

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaSetSize;

int32_t niso_aria_mixin_get_aria_set_size(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_set_size(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaSort

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaSort;

int32_t niso_aria_mixin_get_aria_sort(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_sort(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaValueMax

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaValueMax;

int32_t niso_aria_mixin_get_aria_value_max(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_value_max(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaValueMin

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaValueMin;

int32_t niso_aria_mixin_get_aria_value_min(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_value_min(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaValueNow

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaValueNow;

int32_t niso_aria_mixin_get_aria_value_now(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_value_now(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

ariaValueText

attribute ARIA attribute reflection: Full from ARIAMixin

attribute DOMString? ariaValueText;

int32_t niso_aria_mixin_get_aria_value_text(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_aria_mixin_set_aria_value_text(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

Not in niso yet

Members the web has, by the BCD keys web-features 3.45.0 lists, that idl/ doesn’t declare. The list is partial: web-features lists only the keys it maps to a feature.

• ariaActiveDescendantElement (ARIA attribute reflection)
• ariaControlsElements (ARIA attribute reflection)
• ariaDescribedByElements (ARIA attribute reflection)
• ariaDetailsElements (ARIA attribute reflection)
• ariaErrorMessageElements (ARIA attribute reflection)
• ariaFlowToElements (ARIA attribute reflection)
• ariaLabelledByElements (ARIA attribute reflection)
• ariaOwnsElements (ARIA attribute reflection)
• checkValidity (Form-associated custom elements)
• labels (Form-associated custom elements)
• reportValidity (Form-associated custom elements)
• setFormValue (Form-associated custom elements)
• setValidity (Form-associated custom elements)
• states (:state())
• validationMessage (Form-associated custom elements)
• validity (Form-associated custom elements)
• willValidate (Form-associated custom elements)