eCart produces invalid markup
The latest version of eCart still produces invalid code. Given the idea of these extensions is to save time, more time could be saved quite easily with a few fixes. For example some of the forms close <input> tags correctly; others don't. Eg Add To Cart doesn't close these correctly and uses "POST", instead of "post". Given a page may contain many products, a product page may contain a large number of errors. I don't imagine these errors will prevent a page from working properly but it makes it more difficult to find more serious errors. In any case, I think it's good practice to produce pages which validate.
I've given some examples above, but it's easy to find these and other errors. Eg:
This page contains 79 errors and 42 warnings when run throught the W3 validator. I think both figures should be zero as this is meant to be a professional product.
I appreciate error results will depend on the DOCTYPE, but this is using the DOCTYPE you have chosen. The result is almost the same if Transitional is used rather than Strict anyway.