Extension points

What an application implements, replaces or relies on.

Writing a rule

A rule implements Contract\Rule — id(), criterion(), severity() — and Contract\HtmlRule, Contract\UjoRule or both. It yields a Violation for each problem: a Location, a Message, and, when this case differs from the rule, its own Severity or SuccessCriterion. It holds no state between two contents.

use Phil\AccessibilityCheck\Contract\HtmlRule;
use Phil\AccessibilityCheck\Html\HtmlTarget;
use Phil\AccessibilityCheck\Message;
use Phil\AccessibilityCheck\Severity;
use Phil\AccessibilityCheck\SuccessCriterion;
use Phil\AccessibilityCheck\Violation;

final class NoMarquee implements HtmlRule
{
    public function id(): string
    {
        return 'no-marquee';
    }

    public function criterion(): SuccessCriterion
    {
        return SuccessCriterion::PauseStopHide;
    }

    public function severity(): Severity
    {
        return Severity::Error;
    }

    public function checkHtml(HtmlTarget $target): iterable
    {
        foreach ($target->elements('marquee', 'blink') as $element) {
            yield new Violation($target->locate($element), new Message('no-marquee.found', ['element' => $element->localName]));
        }
    }
}

HtmlTarget gives what a rule asks of the content: elements(...$names), identifiers(), locate(), languageOf(), isHidden(), style(), hasRole(), accessibleName(), labelOf(), textOf(), ownText(), svgTitle(), and policy, language and isFullDocument. UjoTarget gives blocks(...$types) — each a BlockVisit with its block, its pointer, its language and locate() —, fragments(?BlockVisit) — each HTML field as an HtmlTarget located in its block —, and field() and text() to read the data.

Rule\FragmentRule is the base of a rule that reads both: it implements checkUjo() by calling checkBlock() for the data of each block, then checkHtml() for each of its HTML fields.

The rules are given to the checker in the order they run — new AccessibilityChecker($policy, [...DefaultRules::all(), new NoMarquee()()]), or a tagged iterator (Installation). Two rules of one identifier throw InvalidPolicy. Give the rule's messages to the translator (Messages).

The policy

Policy holds the limits, the headings, the contrast, the colours, the languages, the generic link texts and the rules turned off or given another severity: see Policy.

The translator

The checker takes a TranslatorInterface of symfony/translation-contracts: Translation\Messages::translator() by default, to which an application adds the messages of a locale or of a rule, or the translator of the application with Messages::resources() loaded in the domain phil_accessibility_check: see Messages.

The plain fields of UJO

Ujo\PlainFields names, by block type, the fields of the data that never hold HTML — code of a code block, latex and mathml of math, every field of chart (*)… — which the checker does not parse even when they hold a <. A site that registers block types of its own gives the checker its plain fields, replacing the defaults of each type it names:

use Phil\AccessibilityCheck\Ujo\PlainFields;

$checker = new AccessibilityChecker(plainFields: new PlainFields(['recipe' => ['ingredients'], 'chart' => ['*']]));

The content of a subject

Contract\SubjectContent tells the PublicationGuard the HTML or the UJO document of the subject of a workflow: see Publication guard.

The validator and the command

Validator\AccessibleContentValidator and Console\CheckCommand take the AccessibilityChecker they check with: register them as services with the application's checker.

The report

Report, RuleResult, Finding, Location, Message, Severity, SuccessCriterion and ConformanceLevel are values an application reads. The identifiers of the rules, the keys of the messages, the values of Severity and the numbers of SuccessCriterion are stable, so that a report can be stored and read again by them.