How can I write a tab character in Safari? I tried using the tab key with the modifier keys, but I didn't get Safari to write a tab character in a text field shown in an HTML page.

Is it possible to do it? If it is possible, how can I do it?
You can use control-option-tab.

In other applications you can use option-tab, but in Safari tab and option-tab are used to select elements in web views.