Source

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

public function mod_rewrite_rules() {
		if ( ! $this->using_permalinks() ) {
			return '';
		}

		$site_root = parse_url( site_url() );
		if ( isset( $site_root['path'] ) ) {
			$site_root = trailingslashit( $site_root['path'] );
		}

		$home_root = parse_url( home_url() );
		if ( isset( $home_root['path'] ) ) {
			$home_root = trailingslashit( $home_root['path'] );
		} else {
			$home_root = '/';
		}

		$rules  = "<IfModule mod_rewrite.c>\n";
		$rules .= "RewriteEngine On\n";
		$rules .= "RewriteBase $home_root\n";

		// Prevent -f checks on index.php.
		$rules .= "RewriteRule ^index\.php$ - [L]\n";

		// Add in the rules that don't redirect to WP's index.php (and thus shouldn't be handled by WP at all).
		foreach ( (array) $this->non_wp_rules as $match => $query ) {
			// Apache 1.3 does not support the reluctant (non-greedy) modifier.
			$match = str_replace( '.+?', '.+', $match );

			$rules .= 'RewriteRule ^' . $match . ' ' . $home_root . $query . " [QSA,L]\n";
		}

		if ( $this->use_verbose_rules ) {
			$this->matches = '';
			$rewrite       = $this->rewrite_rules();
			$num_rules     = count( $rewrite );
			$rules        .= "RewriteCond %{REQUEST_FILENAME} -f [OR]\n" .
				"RewriteCond %{REQUEST_FILENAME} -d\n" .
				"RewriteRule ^.*$ - [S=$num_rules]\n";

			foreach ( (array) $rewrite as $match => $query ) {
				// Apache 1.3 does not support the reluctant (non-greedy) modifier.
				$match = str_replace( '.+?', '.+', $match );

				if ( strpos( $query, $this->index ) !== false ) {
					$rules .= 'RewriteRule ^' . $match . ' ' . $home_root . $query . " [QSA,L]\n";
				} else {
					$rules .= 'RewriteRule ^' . $match . ' ' . $site_root . $query . " [QSA,L]\n";
				}
			}
		} else {
			$rules .= "RewriteCond %{REQUEST_FILENAME} !-f\n" .
				"RewriteCond %{REQUEST_FILENAME} !-d\n" .
				"RewriteRule . {$home_root}{$this->index} [L]\n";
		}

		$rules .= "</IfModule>\n";

		/**
		 * Filters the list of rewrite rules formatted for output to an .htaccess file.
		 *
		 * @since 1.5.0
		 *
		 * @param string $rules mod_rewrite Rewrite rules formatted for .htaccess.
		 */
		$rules = apply_filters( 'mod_rewrite_rules', $rules );

		/**
		 * Filters the list of rewrite rules formatted for output to an .htaccess file.
		 *
		 * @since 1.5.0
		 * @deprecated 1.5.0 Use the {@see 'mod_rewrite_rules'} filter instead.
		 *
		 * @param string $rules mod_rewrite Rewrite rules formatted for .htaccess.
		 */
		return apply_filters_deprecated( 'rewrite_rules', array( $rules ), '1.5.0', 'mod_rewrite_rules' );
	}