Business rules manual
RGAA v4.1.2
Theme 1: Images
Rule 1.3.4

Rule 1.3.4

Summary

This test consists in checking whether the textual alternative of each object image that convey information is relevant.

Business description

Criterion

1.3

Test

1.3.4

Description

Pour chaque image objet (balise <object> avec l’attribut type="image/…") porteuse d’information , ayant une alternative textuelle ou un contenu alternatif , cette alternative est-elle pertinente (hors cas particuliers)?

  • S’il est présent, le contenu de l’attribut title est pertinent
  • S’il est présent, le contenu de l’attribut WAI-ARIA aria-label est pertinent
  • S’il est présent, le passage de texte associé via l’attribut WAI-ARIA aria-labelledby est pertinent
  • S’il est présent le contenu alternatif est pertinent.

Cas particuliers (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

Decidable with marker

Algorithm

Selection

Set1

All the <object> tags with a type="image" attribute, not within a link and not identified as captcha (see Notes about captcha detection)

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)

Set4

All the elements of Set2 with a textual alternative (see Notes for details about textual alternative detection).

Set5

All the elements of Set3 with a textual alternative (see Notes for details about textual alternative detection).

Process

Test1

For each element of Set4, check whether the content of textual alternative is not relevant (see Notes for details about relevancy test).

For each occurrence of true-result of Test1, raise a MessageA.

For each occurrence of false-result of Test1, raise a MessageB.

Test2

For each element of Set5, check whether the content of textual alternative is not relevant (see Notes for details about relevancy test).

For each occurrence of true-result of Test2, raise a MessageA.

For each occurrence of false-result of Test2, raise a MessageC.

Messages

MessageA
  • code : CheckPresenceOfAlternativeMechanismForInformativeImage
  • status: Pre-Qualified
  • parameter : "title" attribute, "aria-label" attribute, "computed accessible name", "data" attribute, tag name
  • present in source : yes
MessageB
  • code : CheckPertinenceOfAltAttributeOfInformativeImage
  • status: Pre-Qualified
  • parameter : "title" attribute, "aria-label" attribute, "computed accessible name", "data" attribute, tag name
  • present in source : yes
MessageC
  • code : CheckNatureOfImageAndAltPertinence
  • status: Pre-Qualified
  • parameter : "title" attribute, "aria-label" attribute, "computed accessible name", "data" attribute, tag name
  • present in source : yes

Analysis

Not Applicable

The page has no <object> tag with a type="image" attribute with a textual alternative (Set2 is 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 a title attribute

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

For instance, if an aria-label WAI-ARIA attribute and an title attribute 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.

Textual alternative relevancy

The content of the textual alternative is seen as not relevant if :

  • empty
  • only composed of non-alphanumerical characters
  • it has an extension of image type (loaded by the nomenclature named ImageFileExtensions composed of : jpg, gif, jpeg, png, bmp)

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 1.3.3Rule 1.3.5