1. A computer-implemented method for designing a document, said method comprising: displaying a first plurality of selectable items, each selectable item representing a template group comprising a different plurality of related document templates; in response to receiving a user selection of a selectable item representing a particular template group, displaying a second plurality of selectable items representing related document templates of the particular template group, each document template associated with a different plurality of page designs that each specifies a different content layout and rules for formatting content in a page of a document; in response to receiving a user selection of a selectable item representing a particular document template of the particular template group, displaying an editable document comprising a default set of document pages corresponding to a set of page designs in the plurality of page designs associated with the particular document template; after displaying the editable document, replacing at least a portion of the content in a particular page with user generated content; in response to a user action after the editable document is displayed, displaying a third plurality of selectable items representing the plurality of page designs associated with the particular document template; and in response to receiving a selection of a selectable item representing a particular page design, appending the particular page design to the displayed editable document as a document page of the displayed editable document.
14. The method of claim 1 , wherein the appended document page of the displayed editable document is a first new page, the method further comprising: receiving a selection of a different selectable item representing a different page design from the third plurality of page designs associated with said particular document template; and appending said selected different page design to the displayed editable document as a second new page of the displayed editable document that is different from the first new page.