The tooltip like feature that most people are used to seeing when hovering their
cursor over a text link,
is commonly misunderstood as being due to a link having an 'alt' tag. It is true that the 'alt' tag text will display this way, but this is only true for Internet Explorer.
Microsoft has wrongly implemented the 'alt' tag to appear as a tooltip in their Explorer browsers.
Internet Explorer is the only browser which fails to comply with the HTML 4 specification in regard to the appropriate use of the alt attribute. This browser bug has existed for over 11 years, with Internet Explorer's big market share only helping to spread this misconception.
The purpose of an 'alt' tag is to provide a text equivalent for an image, for text only browsers or for browsers set to display no images. It is also vital to screen reader users, who may be unable to physically see an image and so need some sort of text to describe what the image shows. So therefore 'alt' tags should never be used on text links, as they were never designed for this purpose, hence 'alt' standing for 'alternate text' for an image.
The visual tooltip should only appear when there is a 'title' link tag. The purpose of a 'title' tag is to add further explanatory or additional text, for anchor link text that does not specifically convey where the link will take you. A strong emphasis should be placed on the word 'further'. For example, warning users that a link will open a pdf document. A common mistake is to repeat what has been written for the link text.
I recently became aware that a screen reader will first read the link text and then immediately what is contained within the 'title' link tag. So the screen reader user would hear the same bit of information twice. More problematic is that screen readers do not add any pauses between reading out the link text and the 'title' tag text.
A good example of how this can be a problem was highlighted in a RBIB artitle on the misuse of title tags it gave a good example of: "Unless punctuation, or a space has been left between the two, confusion arises because the last word of the TITLE is joined to the first word of the link text. So a link, and TITLE, that both said, “Appearing in Diss” would be delivered as “Appearing in disappearing in Diss”. Most of the time of course it isn’t that neat, and a completely unrecognisable mash of sound is produced."
It is also interesting that a lot of the older automative tools used to check for accessibility insist that every link have a 'title' tag. This view is very outdated, if an anchor link has text that is concise, accurate and clearly informs the user where they will be taken, once a link is clicked. Then there is in fact no need for a