Rule 1.2.5

RGAA v4.0.0

Rule 1.2.5

Summary

This test consists in checking whether the textual alternative of each <canvas> tag is empty or whether aria attributes are well-used to make them ignored by assistive technologies.

Business description

Criterion

1.2

Test

1.2.5

Description

Chaque image bitmap (balise <canvas>) de décoration, sans légende, vérifie-t-elle ces conditions ?

La balise <canvas> possède un attribut WAI-ARIA aria-hidden="true".

La balise <canvas> et ses enfants sont dépourvus d’ alternative textuelle.

Il n’y a aucun texte faisant office d’ alternative textuelle entre <canvas> et </canvas>.

Technical notes (criterion 1.2)

Lorsqu’une image est associée à une légende, la note technique WCAG recommande de prévoir systématiquement une alternative textuelle (cf. critère 1.9). Dans ce cas le critère 1.2 est non applicable.

Dans le cas d’une image vectorielle (balise <canvas>) de décoration qui serait affichée au travers d’un élément <use href="..."> enfant de l’élément <canvas>, le test 1.2.4 s’appliquera également à la balise <canvas> associée par le biais de la balise <use>.

Un attribut WAI-ARIA role="presentation" peut être utilisé sur les images de décoration et les zones non cliquables de décoration. Le rôle "none" introduit en ARIA 1.1 et synonyme du rôle "presentation" peut être aussi utilisé. Il reste préférable cependant d’utiliser le rôle "presentation" en attendant un support satisfaisant du rôle "none".

Level

Technical description

Scope

Page

Decision level

Decidable with marker

Algorithm

Selection

Set1

All the <canvas> tags not identified as captcha (see Notes about captcha detection) and without legend, with an empty textual alternative and without aria mechanism to make them ignored by assistive technologies

css-selector : canvas[aria-hidden=true]:not(a canvas):not([title]):not([aria-label]):not([aria-labelledby]):not(figure:has(figcaption) canvas)

Set2

All the elements of Set1 identified as decorative by marker usage (see Notes for details about detection through marker)

Set3

All the elements of Set1 identified neither as informative, nor as decorative by marker usage (see Notes for details about detection through marker)

Set4

All the <canvas> not within a link and not identified as captcha (see Notes about captcha detection)

css-selector : canvas:not(a canvas):not(figure:has(figcaption) canvas)

Set5

All the elements of Set1 are removed from Set4 :

Set5 = Set4 - Set1

In other words, we keep here all the elements with a not empty textual alternative or without aria mechanism to make them ignored by assistive technologies.

Set6

All the elements of Set5 identified as decorative by marker usage (see Notes for details about detection through marker)

Set7

All the elements of Set5 identified neither as informative, nor as decorative by marker usage (see Notes for details about detection through marker)

Process

Test1

For each element of Set3, raise a MessageA.

Test2

For each element of Set6, raise a MessageB.

Test3

For each element of Set7, raise a MessageC.

Messages

MessageA

code : CheckNatureOfElementWithoutTextualAlternative
status: Pre-Qualified
parameter : text, "aria-label" attribute, "computed accessible name"
present in source : yes

MessageB

code : DecorativeElementWithNotEmptyTextualAlternative
status: Failed
parameter : text, "aria-label" attribute, "computed accessible name"
present in source : yes

MessageC

code : CheckNatureOfElementWithTextualAlternative
status: Pre-Qualified
parameter : text, "aria-label" attribute, "computed accessible name"
present in source : yes

Analysis

Not Applicable

The page has no <canvas> tag (Set1 and Set4 are empty) or they are all marked as informative

Passed

The page only contains <canvas> tags marked as decorative, with an empty textual alternative or with an aria mechanism to make them ignored by assistive technologies : (Set2 is not empty AND Set3 and Set5 are empty)

Failed

At least one <canvas> tag identified as decorative, has a not empty textual alternative (Set6 is not empty)

Pre-qualified

In all other cases

Notes

Textual alternative detection

The textual alternative can be set by the presence of any the following elements :

Text associated via the aria-labelledby WAI-ARIA attribute
Presence of an aria-label WAI-ARIA attribute
Presence of text within the tag

That order has to be respected to compute the textual alternative.

For instance, if an aria-label WAI-ARIA attribute and some text within the tag are both present, the content of the aria-label WAI-ARIA attribute is considered as the textual alternative.

If none of these elements are present, two other conditions exist to set the textual alternative :

A link, or a button is present just before or just after the element
A mechanism exists to let the user replace the element by an alternative content.

Markers

Informative images markers are set through the INFORMATIVE_IMAGE_MARKER parameter.

Decorative images markers are set through the DECORATIVE_IMAGE_MARKER parameter.

The value(s) passed as marker(s) will be checked against the following attributes:

class
id
role

Captcha detection

An element is identified as a CAPTCHA when the “captcha” occurrence is found :

on one attribute of the element
or within the text of the element
or on one attribute of one parent of the element
or within the text of one parent of the element
or on one attribute of a sibling of the element
or within the text of a sibling of the element

Files

Rule 1.2.4 Rule 1.2.6