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Michael said:

> Let me suggest another solution.  My understanding of the
> HTML <alt> tag is slightly different and it certainly does
> appear when the mouse rolls over the image even when one is
> displayed.

I think that depends on browser behaviour.

The img/@alt attribute is required by HTML.

If you have the alt attribute but no title attribute, MSIE (6.0 on Win
2k) displays the value of the alt attribute on mouse-over, but Firefox
(1.02 on Win 2k) (and maybe other Mozilla-based browsers, I haven't
checked) does not.

If you have both alt and title attributes set, MSIE and Firefox both
display the value of the title attribute in preference to the value of
the alt attribute.

I put a page at

http://homes.ukoln.ac.uk/~lispj/temp/alttitle/

to compare the different combinations.

From the HTML 4.01 spec

http://www.w3.org/TR/html401/

(I think these semantics were inherited by XHTML 1.0, but I might be
wrong.)

alt = text [CS]
    For user agents that cannot display images, forms, or applets, this
attribute specifies alternate text. The language of the alternate text
is specified by the lang attribute.

http://www.w3.org/TR/html401/struct/objects.html#adef-alt

title = text [CS]
    This attribute offers advisory information about the element for
which it is set.

Values of the title attribute may be rendered by user agents in a
variety of ways. For instance, visual browsers frequently display the
title as a "tool tip" (a short message that appears when the pointing
device pauses over an object). Audio user agents may speak the title
information in a similar context. For example, setting the attribute on
a link allows user agents (visual and non-visual) to tell users about
the nature of the linked resource:

http://www.w3.org/TR/html401/struct/global.html#adef-title

So I think "alt" is for a textual alternative to the display of the
image and "title" is advisory/supplementary.

I think Michelle's summary here reflects that:

Michelle said:

> Actually I don't think you need go as far as mouseover.  I
> think capturing the legend or title of the dao and outputting
> that as the TITLE attribute in the IMG element should do it
> (not the ALT attribute -- the ALT attribute is what shows up
> if the picture can't/doesn't load).

Pete

-------
Pete Johnston
Research Officer (Interoperability)
UKOLN, University of Bath, Bath BA2 7AY, UK
tel: +44 (0)1225 383619    fax: +44 (0)1225 386838
mailto:[log in to unmask]
http://www.ukoln.ac.uk/ukoln/staff/p.johnston/