In any case, the goal of every author should be to have no errors at all of either kind.Validators typically use a This example uses the HTML5 doctype.Unfortunately, some of these are based on wholly invalid markup and will cause a validator to choke.They'll also lead to display and functionality problems in standards mode.As you fix your markup to remove one error, you may find that you generate more-- or that suddenly several other errors go away.For example, if you add a missing end-table tag () represents data in two dimensions or more.") to a document, you might fix every "element not allowed here" error that followed.Your goal is simple: to bring your page to a state where it doesn't generate any errors at all.
This will happen mostly automagically — provided your browser has the capability — and will look something like what’s shown in Figure 1: Those error messages are browser and OS specific, and hard to modify (which I documented on my blog), but you can change the way the errors appear on the elements themselves with the new validation pseudo-classes, which are part of the CSS3 Basic UI module.
So with all of the boring technical guff out of the way, let’s get on with the interesting technical guff and take a look at some examples of form validation.
One of the most common patterns of validation is that of mandatory (that is, required) values — the fields that the user must complete in order to progress.
One example is wrapping an inline element like element is a generic inline container for phrasing content, which does not inherently represent anything.
It can be used to group elements for styling purposes (using the class or id attributes), or because they share attribute values, such as lang.