1. A method comprising: obtaining a document for display at an electronic device, the document including a content element having an attribute, the attribute being defined in either a body or a header of the document by an associated formatting directive comprising an absolute value referencing a physical characteristic of a display screen; determining that the attribute can be changed for that document based on a presence or absence of an indicator derived from at least one of the body and header; altering the formatting directive to refer to a relative value corresponding to the absolute value, the relative value referencing a base value for the attribute; and rendering the document for display at the electronic device using the formatting directive thus altered.