protected String documentation() {
        if (documentation == null) {
            int cnt = options.length();
            JavaFileObject overviewPath = getOverviewPath();
            if (overviewPath == null) {
                // no doc file to be had
                documentation = "";
            } else {
                // read from file
                try {
                    documentation = readHTMLDocumentation(
                        overviewPath.openInputStream(),
                        overviewPath);
                } catch (IOException exc) {
                    documentation = "";
                    env.error(null, "javadoc.File_Read_Error", overviewPath.getName());
                }
            }
        }
        return documentation;
    }