When the current selection consists of something other than a complete tag (an opening tag, plus a corresponding closing tag if applicable, and the tag's contents), the Quick Tag Editor usually starts in Wrap Tag mode. For example, if the current selection is text with no special formatting, the Quick Tag Editor opens in Wrap Tag mode.
There is one exception to that rule: when the current selection includes an unmatched opening or closing tag, the Quick Tag Editor starts in Edit Tag mode instead of in Wrap Tag mode, and expands the selection to the current selection's parent tag and its contents.
In Wrap Tag mode, you can enter only a single opening tag. If you enter more than one tag, an error message appears and everything you enter is ignored.
When you close the editor, the tag you've entered is inserted at the start of the current selection, and a matching closing tag is inserted at the end of the current selection.
To switch from Wrap Tag mode to Insert HTML mode, use the Control+T (Windows) or Command+T (Macintosh) keyboard shortcut again. See About Insert HTML mode. To switch from Wrap Tag mode to Edit Tag mode, use the keyboard shortcut twice. See About Edit Tag mode.