Excessibility.LiveViewRules.Rule behaviour (Excessibility v0.14.0)

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Behaviour for LiveView-aware accessibility rules.

Each rule inspects a parsed HTML tree (from Floki.parse_document!/1) and returns zero or more findings describing accessibility issues that axe-core cannot detect on its own — typically because the issue depends on Phoenix-specific attributes like phx-click, phx-submit, phx-debounce, etc.

Rules live under lib/excessibility/live_view_rules/rules/ and are auto-discovered at compile time by Excessibility.LiveViewRules.

Implementing a rule

defmodule MyApp.Rules.CustomRule do
  @behaviour Excessibility.LiveViewRules.Rule

  @impl true
  def id, do: :custom_rule

  @impl true
  def default_enabled?, do: true

  @impl true
  def check(tree, _opts) do
    tree
    |> Floki.find("div[phx-click]")
    |> Enum.map(&build_finding/1)
  end

  defp build_finding(element), do: %{...}
end

Register custom rules via application config:

config :excessibility, custom_live_view_rules: [MyApp.Rules.CustomRule]

Summary

Types

finding()

A single finding from a LiveView rule.

severity()

Severity levels for LiveView rule findings.

Callbacks

check(tree, opts)

Inspects the parsed HTML tree and returns any findings.

default_enabled?()

Whether the rule runs by default. Can be overridden via config.

id()

The unique identifier for this rule.

Types

finding()

@type finding() :: %{
  rule: atom(),
  severity: severity(),
  message: String.t(),
  element: String.t(),
  selector: String.t(),
  help: String.t(),
  help_url: String.t() | nil
}

A single finding from a LiveView rule.

severity()

@type severity() :: :critical | :serious | :moderate | :minor

Severity levels for LiveView rule findings.

Callbacks

check(tree, opts)

@callback check(tree :: Floki.html_tree(), opts :: keyword()) :: [finding()]

Inspects the parsed HTML tree and returns any findings.

opts is passed through from Excessibility.LiveViewRules.scan/2 so rules can accept rule-specific options if needed.

default_enabled?()

@callback default_enabled?() :: boolean()

Whether the rule runs by default. Can be overridden via config.

id()

@callback id() :: atom()

The unique identifier for this rule.