Validation
 

I'm new to conversion and am trying to convert my books into Epub. Am using Calibre to do the job, thought I was doing fine as the result seemed legible to me, ran a Validation check using the facility in Sigil, and found a host of problems. May of them read "attribute 'clear' is not declared for element 'br'", some read "hspace" instead of "Clear", one reads "value 'Picture 2' is invalid NCName" and one "The <language> element is missing.". I have absolutely no idea what any of that means. Can anyone tell me if it's fixable, or should I give up and pay someone like Lulu to do it?

You need to post in the epub forum to find out how to create valid epub files. calibre will only produce valid output if you give it valid input

Those are all fixable, but if you don't understand html it's not trivial to fix them.

In many cases Sigil will let you double click on the error in question and it will take you to the source of the error so you can fix it. The 'clear' example is most likely a line in your css that says 'clear' - you can simply delete the line and it will get rid of the error, but it may change your formatting in some areas of the book, you'd need to review it. Similar for hspace.

You might have more luck on the Sigil or epub forum for individual errors - Calibre won't be able to fix these automatically generally speaking, though you could try to do an epub to epub conversion to see if it could eliminate some of them.

I have see it in the body(file): The line reads <br clear="all" />
I simply replace that with a <br /> to make FC happy
clear="all" is valid HTML4.01 , but I have no idea about a valid EPUB?

I'm getting there, which would have been impossible without all the help from this forum. VERY many thanks indeed.