20. A system for enabling in-context authoring of substitute content for one or more non-textual objects, comprising: a memory to access an electronic document comprising content data; and an in-context editor to facilitate in-context editing of substitute content corresponding to a non-textual object, comprising: an interactive input device to select a segment of at least part of the content data, to obtain the non-textual object from a data source and to associate the non-textual object with the content data segment; and an interactive output device to substitute the non-textual object for the content data segment and store the content data segment as the substitute content for the non-textual object.
20. A system for enabling in-context authoring of substitute content for one or more non-textual objects, comprising: a memory to access an electronic document comprising content data; and an in-context editor to facilitate in-context editing of substitute content corresponding to a non-textual object, comprising: an interactive input device to select a segment of at least part of the content data, to obtain the non-textual object from a data source and to associate the non-textual object with the content data segment; and an interactive output device to substitute the non-textual object for the content data segment and store the content data segment as the substitute content for the non-textual object. 23. A system according to claim 20 , wherein the non-textual object is selected from the group comprising graphics, images, icons, controls, applications, audio output, video output, tactile output, MathML, SMIL and subdocuments.