WP_HTML_Tag_Processor::get_attribute( string $name ): string|true|null

Source

public function get_attribute( $name ) {
	if ( self::STATE_MATCHED_TAG !== $this->parser_state ) {
		return null;
	}

	$comparable = strtolower( $name );

	/*
	 * For every attribute other than `class` it's possible to perform a quick check if
	 * there's an enqueued lexical update whose value takes priority over what's found in
	 * the input document.
	 *
	 * The `class` attribute is special though because of the exposed helpers `add_class`
	 * and `remove_class`. These form a builder for the `class` attribute, so an additional
	 * check for enqueued class changes is required in addition to the check for any enqueued
	 * attribute values. If any exist, those enqueued class changes must first be flushed out
	 * into an attribute value update.
	 */
	if ( 'class' === $name ) {
		$this->class_name_updates_to_attributes_updates();
	}

	// Return any enqueued attribute value updates if they exist.
	$enqueued_value = $this->get_enqueued_attribute_value( $comparable );
	if ( false !== $enqueued_value ) {
		return $enqueued_value;
	}

	if ( ! isset( $this->attributes[ $comparable ] ) ) {
		return null;
	}

	$attribute = $this->attributes[ $comparable ];

	/*
	 * This flag distinguishes an attribute with no value
	 * from an attribute with an empty string value. For
	 * unquoted attributes this could look very similar.
	 * It refers to whether an `=` follows the name.
	 *
	 * e.g. <div boolean-attribute empty-attribute=></div>
	 *           ¹                 ²
	 *        1. Attribute `boolean-attribute` is `true`.
	 *        2. Attribute `empty-attribute` is `""`.
	 */
	if ( true === $attribute->is_true ) {
		return true;
	}

	$raw_value = substr( $this->html, $attribute->value_starts_at, $attribute->value_length );

	return WP_HTML_Decoder::decode_attribute( $raw_value );
}

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