Business rules manual
RGAA v4.0.0
Theme 1: Images
Rule 1.3.8

Rule 1.3.8

Summary

This test consists in detecting informative canvas images and thus defining the applicability of the test.

Business description

Criterion

1.3

Test

1.3.8

Description

Pour chaque image bitmap (balise <canvas>) porteuse d’information et ayant un contenu alternatif entre <canvas> et </canvas>, ce contenu alternatif est-il correctement restitué par les technologies d’assistance ?

Particular cases (criterion 1.3)

Il existe une gestion de cas particuliers lorsque l’image est utilisée comme CAPTCHA ou comme image-test. Dans cette situation, où il n’est pas possible de donner une alternative pertinente sans détruire l’objet du CAPTCHA ou du test, le critère est non applicable.

Note : le cas des CAPTCHA et des images-test est traité de manière spécifique par le critère 1.4.

Level

A

Technical description

Scope

Page

Decision level

@@@TODO

Algorithm

Selection

Set1

All the <canvas> tags of the page not within a link and not identified as captcha (see Notes about captcha detection) (css selector : canvas:not(a canvas))

Set2

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

Set3

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

Process

Test1

For each element of Set2, raise a MessageA.

Test2

For each element of Set3, raise a MessageB.

MessageA : Check the pertinence of the alternative of the informative image
  • code : CheckPertinenceOfAltAttributeOfInformativeImage
  • status: Pre-Qualified
  • parameter : text, tag name, snippet
  • present in source : yes
MessageB : Check nature of image and alternative presence and pertinence
  • code : CheckNatureOfImageAndAltPertinence
  • status: Pre-Qualified
  • parameter : text, tag name, snippet
  • present in source : yes

Analysis

Not Applicable

The page has no canvas image (Set1 is empty)

Pre-Qualified

In all other cases

Notes

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 1.3.7Rule 1.3.9