e', __( 'Date', 'wordpress-seo' ), __( 'Replaced with the date of the post/page', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'title', __( 'Title', 'wordpress-seo' ), __( 'Replaced with the title of the post/page', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'parent_title', __( 'Parent title', 'wordpress-seo' ), __( 'Replaced with the title of the parent page of the current page', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'archive_title', __( 'Archive title', 'wordpress-seo' ), __( 'Replaced with the normal title for an archive generated by WordPress', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'sitename', __( 'Site title', 'wordpress-seo' ), __( 'The site\'s name', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'sitedesc', __( 'Tagline', 'wordpress-seo' ), __( 'The site\'s tagline', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'excerpt', __( 'Excerpt', 'wordpress-seo' ), __( 'Replaced with the post/page excerpt (or auto-generated if it does not exist)', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'excerpt_only', __( 'Excerpt only', 'wordpress-seo' ), __( 'Replaced with the post/page excerpt (without auto-generation)', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'tag', __( 'Tag', 'wordpress-seo' ), __( 'Replaced with the current tag/tags', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'category', __( 'Category', 'wordpress-seo' ), __( 'Replaced with the post categories (comma separated)', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'primary_category', __( 'Primary category', 'wordpress-seo' ), __( 'Replaced with the primary category of the post/page', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'category_description', __( 'Category description', 'wordpress-seo' ), __( 'Replaced with the category description', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'tag_description', __( 'Tag description', 'wordpress-seo' ), __( 'Replaced with the tag description', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'term_description', __( 'Term description', 'wordpress-seo' ), __( 'Replaced with the term description', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'term_title', __( 'Term title', 'wordpress-seo' ), __( 'Replaced with the term name', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'searchphrase', __( 'Search phrase', 'wordpress-seo' ), __( 'Replaced with the current search phrase', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'sep', __( 'Separator', 'wordpress-seo' ), $separator_description ),
		);

		foreach ( $replacement_variables as $replacement_variable ) {
			self::register_help_text( 'basic', $replacement_variable );
		}
	}

	/**
	 * Set/translate the help texts for the WPSEO standard advanced variables.
	 */
	private static function set_advanced_help_texts() {
		$replacement_variables = array(
			new WPSEO_Replacement_Variable( 'pt_single', __( 'Post type (singular)', 'wordpress-seo' ), __( 'Replaced with the content type single label', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'pt_plural', __( 'Post type (plural)', 'wordpress-seo' ), __( 'Replaced with the content type plural label', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'modified', __( 'Modified', 'wordpress-seo' ), __( 'Replaced with the post/page modified time', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'id', __( 'ID', 'wordpress-seo' ), __( 'Replaced with the post/page ID', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'name', __( 'Name', 'wordpress-seo' ), __( 'Replaced with the post/page author\'s \'nicename\'', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'user_description', __( 'User description', 'wordpress-seo' ), __( 'Replaced with the post/page author\'s \'Biographical Info\'', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'page', __( 'Page number', 'wordpress-seo' ), __( 'Replaced with the current page number with context (i.e. page 2 of 4)', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'pagetotal', __( 'Pagetotal', 'wordpress-seo' ), __( 'Replaced with the current page total', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'pagenumber', __( 'Pagenumber', 'wordpress-seo' ), __( 'Replaced with the current page number', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'caption', __( 'Caption', 'wordpress-seo' ), __( 'Attachment caption', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'focuskw', __( 'Focus keyword', 'wordpress-seo' ), __( 'Replaced with the posts focus keyphrase', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'term404', __( 'Term404', 'wordpress-seo' ), __( 'Replaced with the slug which caused the 404', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'cf_<custom-field-name>', '<custom-field-name> ' . __( '(custom field)', 'wordpress-seo' ), __( 'Replaced with a posts custom field value', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'ct_<custom-tax-name>', '<custom-tax-name> ' . __( '(custom taxonomy)', 'wordpress-seo' ), __( 'Replaced with a posts custom taxonomies, comma separated.', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'ct_desc_<custom-tax-name>', '<custom-tax-name> ' . __( 'description (custom taxonomy)', 'wordpress-seo' ), __( 'Replaced with a custom taxonomies description', 'wordpress-seo' ) ),
		);

		foreach ( $replacement_variables as $replacement_variable ) {
			self::register_help_text( 'advanced', $replacement_variable );
		}
	}

	/* *********************** GENERAL HELPER METHODS ************************** */

	/**
	 * Remove the '%%' delimiters from a variable string.
	 *
	 * @param string $string Variable string to be cleaned.
	 *
	 * @return string
	 */
	private static function remove_var_delimiter( $string ) {
		return trim( $string, '%' );
	}

	/**
	 * Add the '%%' delimiters to a variable string.
	 *
	 * @param string $string Variable string to be delimited.
	 *
	 * @return string
	 */
	private static function add_var_delimiter( $string ) {
		return '%%' . $string . '%%';
	}

	/**
	 * Retrieve a post's terms, comma delimited.
	 *
	 * @param int    $id            ID of the post to get the terms for.
	 * @param string $taxonomy      The taxonomy to get the terms for this post from.
	 * @param bool   $return_single If true, return the first term.
	 *
	 * @return string Either a single term or a comma delimited string of terms.
	 */
	public function get_terms( $id, $taxonomy, $return_single = false ) {

		$output = '';

		// If we're on a specific tag, category or taxonomy page, use that.
		if ( is_category() || is_tag() || is_tax() ) {
			$term   = $GLOBALS['wp_query']->get_queried_object();
			$output = $term->name;
		}
		elseif ( ! empty( $id ) && ! empty( $taxonomy ) ) {
			$terms = get_the_terms( $id, $taxonomy );
			if ( is_array( $terms ) && $terms !== array() ) {
				foreach ( $terms as $term ) {
					if ( $return_single ) {
						$output = $term->name;
						break;
					}
					else {
						$output .= $term->name . ', ';
					}
				}
				$output = rtrim( trim( $output ), ',' );
			}
		}
		unset( $terms, $term );

		/**
		 * Allows filtering of the terms list used to replace %%category%%, %%tag%% and %%ct_<custom-tax-name>%% variables.
		 *
		 * @api    string    $output    Comma-delimited string containing the terms.
		 * @api    string    $taxonomy  The taxonomy of the terms.
		 */
		return apply_filters( 'wpseo_terms', $output, $taxonomy );
	}
} /* End of class WPSEO_Replace_Vars */