Opens a dialog which allows to add a new view to current document tab. A document tab can contain up to 5 views: default central view, but also top, right, bottom, left views. A view is specified by selecting a CSS style sheet among the available ones or, on the contrary, by selecting no style sheet at all, which implies to use a tree view.
Closes active view. Central view, which is supposed to be the main view, cannot be closed.
The active view is the view having the keyboard focus: the caret blinks in this view, and not in the other views of the document. To make a view the active one, simply click anywhere in it.
Below the above menu item, a menu item is added for each CSS style sheet available for current document. Selecting the name of a style sheet causes the document view to use this style sheet. If a document view already uses the selected style sheet, the style sheet is reloaded from its file (which is very handy when developing a new CSS style sheet).