Chez Augustin

1) Remember that Drupal does not always output what you inputted: it adds <p> and <br /> where you would not expect. The validation services checks what Drupal outputs, not what you wrote.

2) On the validation page, you can check one or more options at the top,
and then click the 'revalidate' button. One that is useful is the 'show source', so that you can see the actual code is being validated (the one outputted by Drupal). With 'show source' selected, you can click on the line number and see where the problem is.

3) Don't be intimidated by the number of errors. Once single error can start a chain reaction and cascade down the code. Always start with the first error, and solving it often reduces the number of errors by a few dozens!