Source

File: wp-includes/class-wp-taxonomy.php

public function set_props( $object_type, $args ) {
		$args = wp_parse_args( $args );

		/**
		 * Filters the arguments for registering a taxonomy.
		 *
		 * @since 4.4.0
		 *
		 * @param array    $args        Array of arguments for registering a taxonomy.
		 * @param string   $taxonomy    Taxonomy key.
		 * @param string[] $object_type Array of names of object types for the taxonomy.
		 */
		$args = apply_filters( 'register_taxonomy_args', $args, $this->name, (array) $object_type );

		$defaults = array(
			'labels'                => array(),
			'description'           => '',
			'public'                => true,
			'publicly_queryable'    => null,
			'hierarchical'          => false,
			'show_ui'               => null,
			'show_in_menu'          => null,
			'show_in_nav_menus'     => null,
			'show_tagcloud'         => null,
			'show_in_quick_edit'    => null,
			'show_admin_column'     => false,
			'meta_box_cb'           => null,
			'meta_box_sanitize_cb'  => null,
			'capabilities'          => array(),
			'rewrite'               => true,
			'query_var'             => $this->name,
			'update_count_callback' => '',
			'show_in_rest'          => false,
			'rest_base'             => false,
			'rest_controller_class' => false,
			'default_term'          => null,
			'_builtin'              => false,
		);

		$args = array_merge( $defaults, $args );

		// If not set, default to the setting for 'public'.
		if ( null === $args['publicly_queryable'] ) {
			$args['publicly_queryable'] = $args['public'];
		}

		if ( false !== $args['query_var'] && ( is_admin() || false !== $args['publicly_queryable'] ) ) {
			if ( true === $args['query_var'] ) {
				$args['query_var'] = $this->name;
			} else {
				$args['query_var'] = sanitize_title_with_dashes( $args['query_var'] );
			}
		} else {
			// Force 'query_var' to false for non-public taxonomies.
			$args['query_var'] = false;
		}

		if ( false !== $args['rewrite'] && ( is_admin() || get_option( 'permalink_structure' ) ) ) {
			$args['rewrite'] = wp_parse_args(
				$args['rewrite'],
				array(
					'with_front'   => true,
					'hierarchical' => false,
					'ep_mask'      => EP_NONE,
				)
			);

			if ( empty( $args['rewrite']['slug'] ) ) {
				$args['rewrite']['slug'] = sanitize_title_with_dashes( $this->name );
			}
		}

		// If not set, default to the setting for 'public'.
		if ( null === $args['show_ui'] ) {
			$args['show_ui'] = $args['public'];
		}

		// If not set, default to the setting for 'show_ui'.
		if ( null === $args['show_in_menu'] || ! $args['show_ui'] ) {
			$args['show_in_menu'] = $args['show_ui'];
		}

		// If not set, default to the setting for 'public'.
		if ( null === $args['show_in_nav_menus'] ) {
			$args['show_in_nav_menus'] = $args['public'];
		}

		// If not set, default to the setting for 'show_ui'.
		if ( null === $args['show_tagcloud'] ) {
			$args['show_tagcloud'] = $args['show_ui'];
		}

		// If not set, default to the setting for 'show_ui'.
		if ( null === $args['show_in_quick_edit'] ) {
			$args['show_in_quick_edit'] = $args['show_ui'];
		}

		$default_caps = array(
			'manage_terms' => 'manage_categories',
			'edit_terms'   => 'manage_categories',
			'delete_terms' => 'manage_categories',
			'assign_terms' => 'edit_posts',
		);

		$args['cap'] = (object) array_merge( $default_caps, $args['capabilities'] );
		unset( $args['capabilities'] );

		$args['object_type'] = array_unique( (array) $object_type );

		// If not set, use the default meta box.
		if ( null === $args['meta_box_cb'] ) {
			if ( $args['hierarchical'] ) {
				$args['meta_box_cb'] = 'post_categories_meta_box';
			} else {
				$args['meta_box_cb'] = 'post_tags_meta_box';
			}
		}

		$args['name'] = $this->name;

		// Default meta box sanitization callback depends on the value of 'meta_box_cb'.
		if ( null === $args['meta_box_sanitize_cb'] ) {
			switch ( $args['meta_box_cb'] ) {
				case 'post_categories_meta_box':
					$args['meta_box_sanitize_cb'] = 'taxonomy_meta_box_sanitize_cb_checkboxes';
					break;

				case 'post_tags_meta_box':
				default:
					$args['meta_box_sanitize_cb'] = 'taxonomy_meta_box_sanitize_cb_input';
					break;
			}
		}

		// Default taxonomy term.
		if ( ! empty( $args['default_term'] ) ) {
			if ( ! is_array( $args['default_term'] ) ) {
				$args['default_term'] = array( 'name' => $args['default_term'] );
			}
			$args['default_term'] = wp_parse_args(
				$args['default_term'],
				array(
					'name'        => '',
					'slug'        => '',
					'description' => '',
				)
			);
		}

		foreach ( $args as $property_name => $property_value ) {
			$this->$property_name = $property_value;
		}

		$this->labels = get_taxonomy_labels( $this );
		$this->label  = $this->labels->name;
	}