Re: show_help_echo truncates unconditionally

[Richard Stallman]

    It is called to display information stored in the help-echo property
    of strings.  For example moving the mouse pointer over the mode-line,
    menu entries or some buttons, buffer lines in grep-mode.  Normaly
    show_help_echo delegates all work to show-help-function.  This
    mechanism is used to popup tooltips.  When show-help-function is nil
    (like on text only displays or when tooltip-mode is disabled)
    show_help_echo does the job itself by displaying those strings in the
    echo-area.

Could someone please clarify the comment based on this?
The existing comment was not written with a view to making
it clear to people who don't already know.