Hello,
In the appendix I, page 601, the img attribute longdesc is mentioned as an obsolete attribute.
Although, as you can see at the link hereafter, the W3C does not seem to consider it as obsolete: http://www.w3.org/TR/html-longdesc/
Is there an error in the book or is there any other documentation that tell us that this attribute is obsolete?
Thank you in advance for your answer.
Kind regards.

So sorry I missed this before. If I remember the timing correctly, longdesc, at the time of writing, had been removed from the HTML5 specification. People didn't like that and lobbied for its return. longdesc fans eventually won. As it stands the book is in error (although it wasn't when I wrote it.)

Again, sorry for being so slow to reply, I've had a busy few weeks.