String concatenation
====================

Could skip standard string concatenation (it doesn't work well with memory
allocation anyway), and use template strings and string builders for that
purpose.

    String id = get_id void
    String button_html = make_button_html void
    StringBuilder sb = t"<div id={id}>"
    sb.append message
    sb.append "<br>Message length: {length message}"
    sb.append_with_unchecked t"{button_html:raw}"
    sb.append t"</div>"
    return sb.to_html_string  # <-- extension method

Pure string builder, with no escape handling:

    StringBuilder sb = "<a"
    sb.append " rel=nofollow"
    sb.append " href=https://example.com/"
    sb.append ">"
    return sb.to_raw_unchecked_string
    # or
    return sb.to_ascii_printable_string